Study on the comparison of the pyrolysis gas release of lignite and its briquette

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高一英语学术研究方法单选题40题

高一英语学术研究方法单选题40题1. What is a research hypothesis?A. A statement that is always true.B. A prediction about the relationship between variables.C. A conclusion based on research findings.D. A question that needs to be answered.答案：B。

选项A，研究假设不是总是正确的陈述。

选项C，研究假设是在研究之前做出的预测，不是基于研究发现的结论。

选项D，研究假设不是一个需要回答的问题，而是对变量之间关系的预测。

2. What is a literature review?A. A summary of all the books on a topic.B. A critical analysis of existing research on a topic.C. A collection of research papers.D. A list of research questions.答案：B。

选项A，文献综述不仅仅是对一个主题的所有书籍的总结。

选项C，文献综述不是简单的研究论文集合。

选项D，文献综述不是研究问题列表。

3. What is a research method?A. A way to collect data.B. A theory about a topic.C. A conclusion from research.D. A list of research questions.答案：A。

选项B，研究方法不是关于一个主题的理论。

选项C，研究方法不是研究得出的结论。

选项D，研究方法不是研究问题列表。

4. What is a sample in research?A. A part of the population being studied.B. The entire population.C. A list of research questions.D. A research method.答案：A。

小学下册第4次英语第二单元期末试卷(含答案)

小学下册英语第二单元期末试卷(含答案)英语试题一、综合题(本题有100小题，每小题1分，共100分.每小题不选、错误，均不给分)1.The chemical symbol for lithium is ____.2.The kitten is very ______ (curious).3.Who is the author of "Harry Potter"?A. J.K. RowlingB. Roald DahlC. Mark TwainD. Agatha Christie4.The _____ (大树) provides shade in the summer.5.My mom enjoys __________ (制作) crafts with me.6.I like to help my dad in the ____.7.What is the smallest unit of life?A. OrganB. TissueC. CellD. Organism答案:C8.What do you use to write on paper?A. BrushB. PencilC. RulerD. Eraser答案:B9.My cousin is a ______. She loves to play with dogs.10. A __________ (化学比赛) fosters interest and knowledge among students.11. A ________ (小岛) is smaller than an island.12.My brother collects ____ (coins) from around the world.13.The _____ (花卉) industry provides many jobs.14.What sound does a dog make?A. MeowB. BarkC. MooD. Quack15.The ________ (symposium) features experts.16.How many players are on a soccer team?A. 10B. 11C. 12D. 1317.The chemical reaction between baking soda and vinegar produces _______.18.What do you call the liquid that comes from trees?A. GumB. SyrupC. SapD. Juice答案:C19.What is the name of the river that runs through Egypt?A. NileB. AmazonC. YangtzeD. Mississippi答案:A20.What is the primary ingredient in pancakes?A. FlourB. SugarC. EggsD. Milk答案:A21.What is the main ingredient in salad?A. BreadB. VegetablesC. MeatD. Rice答案:B22.__________ (化肥) provide essential nutrients for plants.23.The ______ is a plant that can grow very tall.24.ts can survive in ______ (沙漠). Some pla25.The __________ (生态平衡) is vital for our planet.26.Which of these is a type of weather?A. HappyB. RainC. FastD. Bright27.My favorite toy is a ______ (玩具名). It is very ______ (形容词). I play with it every day. Sometimes, I take it to the ______ (地方).28.What is the main ingredient in cookies?A. SugarB. FlourC. ButterD. All of the above29.The first woman to vote in the United States was ______ (苏珊·安东尼).30.What do we call a person who helps sick people?A. TeacherB. NurseC. EngineerD. Chef31.The main use of citric acid is in _____.32.What is 3 x 3?A. 6B. 7C. 8D. 933. A starfish can live in both ______ (海洋) and freshwater.34.My aunt, ______ (我的姑姑), is an amazing teacher.35.What is the capital city of Nicaragua?A. ManaguaB. LeónC. GranadaD. Masaya36.She rides her ______ to school. (bike)37.I have a toy _______ that can spin and twirl.38.What do you call the time of year when leaves fall from trees?A. SpringB. SummerC. FallD. Winter答案:C39.The ocean is ________ (广阔).40.The __________ is known for its diverse cultures.41.The process of filtration separates solids from ______.42.My sister enjoys __________ (参加工作坊).43.What do we call a person who studies ancient civilizations?A. ArchaeologistB. HistorianC. AnthropologistD. Geologist44.What do you call a story that is told using pictures?A. NovelB. ComicC. BiographyD. Poem答案:B45.What do we call a scientist who studies the weather?A. MeteorologistB. ClimatologistC. GeologistD. Astronomer答案:A46.are a famous ________ (阿尔卑斯山是一座著名的________) range in Europe. The Amaz47.The _____ (oranges) are fresh.48. A _____ (猫头鹰) hoots at night.49. A ______ (狮子) lives in prides with its family.50.The __________ (化学稳定性) of a substance refers to its resistance to change.51.She has a nice ________.52.can Revolution was influenced by Enlightenment ________ (理念). The Amer53.The garden is _______ (充满生机的)。

2022年考研考博-考博英语-中国财政科学研究院考试预测题精选专练VII(附带答案)卷9

2022年考研考博-考博英语-中国财政科学研究院考试预测题精选专练VII（附带答案）第1套一.综合题(共25题)1.单选题______ that as both birds and mammals become larger, their metabolic rates per unit of tissue decrease, and they generally live longer.问题1选项A.The truthB.It is trueC.If trueD.To be true【答案】B【解析】考查固定句型。

句意：的确，随着鸟类和哺乳动物的体型变大，它们每单位组织的代谢率会下降，它们通常会活得更长。

It is/was+adj.+that是强调句型，It作形式主语，真正主语是that 后面的内容，B选项It is true符合题意。

因此B选项正确。

2.单选题While the company’s CEO professes to be confident and urges the deal forward, its investors are unlikely to be so _______ about its prospects. Many were uncomfortable at the way the corporation was forced to spend much of its capital in last year’s expansion, and this new venture is potentially even more risky.问题1选项A.apatheticB.sanguineC.apprehensiveD.anxious【答案】B【解析】考查形容词辨析。

A选项apathetic“无动于衷的；缺乏兴趣的”；B选项sanguine“乐观的，充满希望的”；C选项apprehensive“忧虑的”；D选项anxious“担忧的；急切的”。

氧化铁与碳酸钾对煤温和气化的影响

第16卷第2期化学反应工程与工艺 Vo l16,N o2 2000年6月 Chemica l R ea ct ion Engineer ing and T echnolog y June,　2000文章编号:1001-7631(2000)02-0203-06研究简报氧化铁与碳酸钾对煤温和气化的影响朱廷钰1,王　洋2(1.中国科学院工程热物理研究所,北京100080;2.中国科学院山西煤炭化学研究所气化室,山西太原030001)摘　要:　对神木煤进行了流化床煤温和气化研究,考察了氧化铁、碳酸钾对煤温和气化产物产率、气体组成、半焦组成的影响。

试验结果表明:添加氧化铁后,煤气中H2产率显著增加,CO产率明显下降。

添加碳酸钾后,H2产率增幅较小,CO、CH4及其它气态烃产率基本不变,表明碳酸钾对烃类裂解反应无明显催化作用。

通过对所得半焦组成分析,发现添加碳酸钾所得半焦中硫、氮含量比原煤热解半焦有所增加,添加氧化铁所得半焦中硫、氮含量无明显变化。

关键词:氧化铁;碳酸钾;温和气化;流化床反应器中图分类号:TQ54　文献标识码:A1　前　言能源是经济发展的基础和关键,所以世界能源形式影响着各国政治经济动向。

二次世界大战之后石油消耗剧增。

1973年石油涨价之后,人们开始注意到,石油储量少,而煤炭储量高达1.1×1013吨,远比石油储量大。

因此,近几十年来世界有关煤炭利用的新技术和新理论层出不穷,煤科学得到很大发展。

煤在化学上和物理上是非均相的矿物或岩石,主要含有碳、氢、氧以及少量硫和氮,其它组成是成灰的无机化合物,它们以矿物质分散颗粒分布在整个煤中[1]。

煤是我国主要能源,煤炭占能源消费比重较大,但煤炭热利用率仅为30%左右。

化学工业以煤化工起家,现在虽然采用大力发展石油化工的方针,但煤化工在现在和将来相当长一段时间内仍将起着主要作用。

可是传统煤转化技术由于能耗高、污染大、效率低,已远远不能满足社会发展的需要。

homo sapiens and pan troglodytes 雅思阅读题库

homo sapiens and pan troglodytes 雅思阅读题库Homo sapiens and Pan troglodytes: A Comparative StudyIntroductionIn the field of anthropology and evolutionary biology, the comparison between Homo sapiens (humans) and Pan troglodytes (chimpanzees) has been a subject of great interest. Both species belong to the family Hominidae, commonly known as the great apes, and share a significant amount of genetic material. This article aims to explore the similarities and differences between Homo sapiens and Pan troglodytes, highlighting their evolutionary history, physical characteristics, and cognitive abilities.Evolutionary History1. Common AncestryHomo sapiens and Pan troglodytes shared a common ancestor that lived approximately 6 to 8 million years ago. This common ancestor is believed to be a hominid that resided in the African continent.2. Divergence and SpeciationOver time, evolutionary changes led to the divergence of Homo sapiens and Pan troglodytes. While humans continued to evolve with advancing cognitive abilities, the chimpanzees followed a different evolutionary path.Physical Characteristics1. Body StructureBoth Homo sapiens and Pan troglodytes possess similar anatomical features, such as an upright posture, opposable thumbs, and five-digit limbs. However, humans have a distinctively longer and more vertically aligned spine, allowing for efficient bipedal locomotion.2. Brain Size and Skull StructureHomo sapiens have a significantly larger brain size compared to Pan troglodytes. The increased brain size in humans is associated with advanced cognitive functions, language abilities, and complex social behaviors. Additionally, human skulls have a more rounded shape, while chimpanzee skulls exhibit a prominent brow ridge.3. Facial FeaturesHumans possess a relatively flat face with reduced prognathism (outward protrusion of the lower face). In contrast, chimpanzees have a prominent jaw and snout-like projection, enabling them to exert greater force during feeding and social interactions.Cognitive Abilities1. Tool Use and ManufacturingBoth Homo sapiens and Pan troglodytes exhibit advanced tool use. However, humans have demonstrated more sophisticated tool manufacturing and complex problem-solving skills, which have contributed to our ability to adapt to various environments.2. Language and CommunicationOne of the most significant distinguishing factors is the ability of Homo sapiens to develop complex languages. Our communication systems involve intricate grammar, syntax, and abstract reasoning. While chimpanzees possess a basic form of vocal communication and the ability to use sign language, their linguistic abilities remain limited in comparison.3. Social Structures and CooperationBoth species exhibit complex social structures, with hierarchical systems and cooperative behaviors. However, humans display more intricate social norms, cultural diversity, and the capacity for organized societies on a global scale.ConclusionThe comparative study of Homo sapiens and Pan troglodytes provides valuable insights into our evolutionary relationship and highlights the distinctive characteristics that set humans apart. While both species share common ancestry and certain physical traits, Homo sapiens have undergone significant evolutionary changes, leading to advanced cognitive abilities, complex language development, and higher levels of social organization. Understanding these similarities and differences enhances our understanding of human evolution and the complexities surrounding our place within the animal kingdom.。

基于Aspen_Plus的循环流化床工业气化炉模拟

2018年第37卷第5期 CHEMICAL INDUSTRY AND ENGINEERING PROGRESS·1709·化工进展基于Aspen Plus 的循环流化床工业气化炉模拟刘忠慧1，2，于旷世1，张海霞1，朱治平1，2（1中国科学院工程热物理研究所，北京 100190；2中国科学院大学，北京 100049）摘要：循环流化床煤气化炉在工业应用过程中，由于试验煤种及操作条件的多样性，通过试验法优化操作过程所需周期较长、成本较大。

因此以大量工程数据为边界条件，基于Gibbs 自由能最小化原理，利用Aspen Plus 对气化过程进行模拟，通过灵敏度分析，研究了单因素氧煤比、蒸汽煤比、气化压力、空气/蒸汽预热温度变化对气化指标的影响；并运用正交实验，研究了以上4种因素共同作用的结果。

研究结果表明：氧煤比增加使有效气（CO+H 2）含量、冷煤气效率先增加再减小，并在0.45～0.50kg/kg 时取得最大值；蒸汽煤比增加使煤气热值和气化温度减小，对有效气含量基本没有影响；气化压力增加使煤气热值和气化温度增加；空气/蒸汽预热温度增加使气化温度、有效气含量、冷煤气效率增加，煤气热值减小。

通过正交实验综合分析，氧煤比和空气/蒸汽预热温度对气化指标的影响较为显著，两者对气化指标的影响趋势基本一致；蒸汽煤比主要影响煤气热值，而气化压力主要影响比氧耗，对其他指标影响较小。

关键词：循环流化床；优化；Aspen Plus ；灵敏度分析；正交实验中图分类号：TQ546 文献标志码：A 文章编号：1000–6613（2018）05–1709–09 DOI ：10.16085/j.issn.1000-6613.2017-1493Simulation of industrial circulating fluidized bed gasifier by Aspen PlusLIU Zhonghui 1，2，YU Kuangshi 1，ZHANG Haixia 1，ZHU Zhiping 1，2（1Institute of Engineering Thermophysics ，Chinese Academy of Sciences ，Beijing 100190，China ；2University of ChineseAcademy of Sciences ，Beijing 100049，China ）Abstract ：In the process of industrial circulating fluidized bed gasification ，experimental research is time-consuming and cost-consuming due to the diversity of coal types and operating conditions. A circulating fluidized bed gasifier model was developed by Aspen Plus based on Gibbs free energy minimization. The boundary conditions of the simulation were set in terms of existing industry data. Different factors in gasification process were investigated ，including oxygen-coal ratio ，stream-coal ratio ，gasification pressure and air/stream preheating temperature. The orthogonal experiments were used to study the interactive effect of the four factors. The results showed that the gasification product （CO+H 2） content and cold gas efficiency increase first and then decrease with oxygen-coal ratio increasing. The optimal range of oxygen-coal ratio is 0.45—0.50kg/kg. The gas heating value and gasification temperature decrease with the increase of stream-coal ratio. However ，the gasification product content is hardly affected by stream-coal ratio. The gas heating value and gasification temperature increase with gasification pressure increasing. The gasification temperature ，gasification product content and cold gas efficiency increase with air/stream preheating temperature increasing ，while gas heating value decreases with air/stream preheating temperature increasing. The oxygen-coal工艺模拟与优化。

高中英语学术前沿单选题30题

高中英语学术前沿单选题30题1. In academic research, the data should be analyzed ______ to draw accurate conclusions.A. carefullyB. carelesslyC. quicklyD. slowly答案：A。

本题考查副词的用法。

carefully 表示“仔细地”，在学术研究中，为了得出准确的结论，数据应该被仔细分析。

carelessly 表示“粗心地”，不符合学术研究的要求。

quickly 表示“快速地”，但重点不是速度而是仔细程度。

slowly 表示“缓慢地”，也不符合学术研究追求准确的目的。

2. The scientist ______ a new theory to explain the phenomenon.A. put forwardB. put offC. put upD. put down答案：A。

put forward 意为“提出”，科学家提出新理论来解释这一现象，符合语境。

put off 表示“推迟”；put up 表示“张贴；搭建”；put down 表示“写下；镇压”，均不符合。

3. The experiment was ______ because of the lack of funds.A. cancelledB. continuedC. completedD. controlled答案：A。

cancelled 表示“取消”，由于缺乏资金实验被取消。

continued 表示“继续”；completed 表示“完成”；controlled 表示“控制”，均不符合缺乏资金的情况。

4. The results of the study ______ the previous hypothesis.A. confirmedB. contradictedC. supportedD. ignored答案：B。

锦州Unit,24年小学三年级下册第16次英语第1单元真题试卷[有答案]

锦州Unit,24年小学三年级下册英语第1单元真题试卷[有答案]考试时间：100分钟（总分:100）B卷考试人：_________题号一二三四五总分得分一、综合题(共计100题)1、听力题：A chemical reaction can release _____ as a product.2、填空题：A ______ (青蛙) can leap far distances.3、填空题：The _____ (果实) develops after flowers bloom.4、填空题：The dolphin is very _______ (聪明) and playful.5、What do you call a person who plays music?A. MusicianB. SingerC. PerformerD. All of the above答案:D6、听力题：Chemists study the properties of _____ and their interactions.7、听力题：A chemical reaction can produce a precipitate from ______.8、填空题：I want to be a __________ (作家) when I grow up.9、填空题：A _______ (海马) has a unique swimming style.10、听力题：Chemical bonds are formed through the sharing or transfer of ______.11、听力题：I have a ___ (pen/pencil) in my bag.12、听力题：The chemical symbol for carbon is ______.13、听力题：The __________ is a famous mountain range in North America.14、填空题：During my free time, I enjoy ______ (画画) or playing video games. It’s a good way to relax.15、填空题：The _______ (The Gold Rush) brought many settlers to California in the 1840s.16、听力题：The main component of air is _____.17、填空题：We have a ______ (丰富的) series of events planned.18、填空题：The nurse gives _____ (疫苗) to children.19、听力题：Light-years measure the distance that light travels in a ______.20、填空题：A _____ (种子) can grow into a new plant.21、听力题：A solar system consists of a star and all its ______.22、听力题：The Voyager spacecraft have traveled beyond the _______ of our solar system.23、填空题：My favorite way to relax is _______ (听音乐).24、What is the name of the famous wizarding school in Harry Potter?A. HogwartsB. NarniaC. OzD. Middle-Earth答案:A25、What sound does a cow make?A. MeowB. BarkC. MooD. Quack答案: C26、听力题：The fish swims in the _______ (water).27、填空题：A garden is full of __________ (生命).28、听力题：The study of rocks can reveal information about the Earth's ______.29、填空题：A _____ (兔子) can hop very fast.30、Which shape has four equal sides?a. Triangleb. Rectanglec. Squared. Circle答案:c31、填空题：I have a special place for my ____.32、填空题：My favorite superhero is _______ (名字). 他/她的能力是 _______ (能力).33、填空题：My ________ (玩具名称) is made of plastic and metal.34、What do we call the soft part of the bread?A. CrustB. CrumbC. LoafD. Slice35、听力题：The ______ is a talented musician.36、填空题：The owl sleeps during the _________. (白天)37、填空题：The _____ (turf) provides a soft lawn.38、填空题：The cheetah is built for _________. (速度)39、选择题：What is 50 - 25?A. 15B. 20C. 25D. 3040、听力题：The __________ is a region known for its societal structures.41、填空题：I like to go ________ (滑雪) during winter holidays.42、听力题：The chemical symbol for copper is _____.43、听力题：The Earth's crust is continuously undergoing ______.44、填空题：The ________ (植物选育) leads to better yields.45、What is the capital of Australia?A. SydneyB. MelbourneC. CanberraD. Brisbane46、填空题：The _______ (Spanish Flu) pandemic occurred in 1918-1919.47、What is the name of the largest land animal?A. HippoB. RhinoC. ElephantD. Giraffe答案: C48、听力题：My favorite color is ______. (blue)49、What do we call a person who writes books?A. AuthorB. ReaderC. EditorD. Publisher50、听力题：The stars are _____ (bright/dim) at night.51、听力题：A ______ can glide through the air.52、听力题：Air is a mixture of several different ______.53、填空题：A _____ (小马) can be very gentle with children.54、填空题：My ________ (玩具名称) has a funny voice.55、What is 7 + 2?A. 8B. 9C. 10D. 1156、填空题：I have a wonderful . (我有一个美好的。

多胺树脂催化合成增塑剂

摘要：以聚氯乙烯和多乙烯多胺为原料合成了聚氯乙烯一乙烯多胺树脂，用红外光谱对多胺树脂结构进行多并了表征。再以聚氯乙烯一乙烯多胺树脂为催化剂，多以柠檬酸和正丁醇为原料，苯作带水剂，１５１０℃ 回在１～４流反应，成了柠檬酸三丁酯。研究了催化剂用量、合原料配比、应时间及带水剂用量等因素对反应的影响，反并对树脂催化剂的重复使用性能进行了研究。结果表明，塑剂的最佳合成条件为（）：（）增酸醇一１：，４树
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１０１０目，州化工厂；Ｐ，２～６株ＰＷ≥ ９，０１５１１５５Ｃ，昌试剂三厂。．０～．０，Ｐ宜一

关于假说的英文作文题目

关于假说的英文作文题目英文：As a student, I have always been fascinated by the concept of hypothesis. A hypothesis is essentially an educated guess or a proposed explanation for a phenomenon. It is a crucial part of the scientific method, as it provides a starting point for further investigation and experimentation.One classic example of a hypothesis is the statement "the higher the temperature, the faster the water will boil." This hypothesis can be tested by conducting an experiment in which water is heated to different temperatures and the time it takes to boil is recorded. If the results consistently support the hypothesis, it can be considered valid.Another example is the hypothesis that "plants will grow taller if they receive more sunlight." This can betested by placing identical plants in different light conditions and measuring their growth over time. If the plants exposed to more sunlight indeed grow taller, the hypothesis is supported.Hypotheses can also be used in everyday life. For instance, if I hypothesize that studying for an extra hour each day will improve my grades, I can test this by implementing the study habit and monitoring my academic performance. If my grades do improve, it would provide evidence in support of my hypothesis.In Chinese, 假设是科学研究中的一个重要环节，它是对某一现象的推测或者解释。

学术英语习题及部分问题详解

Training and Practice for English for Academic PurposesPart I1.Discuss the following questions.What are basic principles the researchers must try to follow when they write their research papers? And would you please list some deadly sins a researcher must avoid when they want to publish a research paper? What are the main contents of a research paper?2. Translate the following Chinese introduction into English.提高起重机生产力和安全性的设备研究近些年来，就用研究人员对起重机(crane)的研究兴趣与日俱增。

起重机种类繁多，从樱桃采摘机(cherry pickers)到巨型塔式起重机(huge tower cranes) ，是建筑工地不可或缺的重要设备之一。

由于建筑用起重机工作环境多变(constantly changing working environment), 操作者(operator)责任重大(heavy reliance)。

过去几十年里，超重机技术日新月异，但是操作员与其他工种人员配合协作方面的技术发展缓慢。

起重机的发展步伐如此迅猛，我们似乎要问，在某些方面，是不是已经超出(outstrip)了人们安全使用的能力？本文旨在探讨如何通过新型设备的引进提高起重机生产力以及提出相关安全性的举措，进而为新型起重机的应用和案例提供新的思路。

In recent years, researchers have become more interested in crane research. The variety of cranes, from cherry pickers to giant tower cranes, is one of the most important equipment on construction sites. As a result of the changing working environment of the construction crane, operator is responsible for heavy reliance. Over the past few decades, the technology of overweight machines has been changing rapidly, but the operators have been slow to cooperate with other workers in collaboration. The pace of development of cranes is so rapid that we seem to be asking whether in some respects, the outstrip has exceeded the ability of people to safely use it. This paper aims to explore how to improve crane productivity and raise related security measures through the introduction of new equipment, so as to provide new ideas for the application and case of new cranes.3. You are writing a research paper entitled “The Effects of Radiation from the Sun on Life on Earth”. In your introduction you need to review, in general terms, how the sun supports life on the earth. Prepare an Introduction section for your paper based on the information below.⏹Distance from the earth: 92,976,000 miles⏹The Sun’s energy comes from nuclear fusion of hydrogen to helium.⏹Intense radiation, including lethal ultraviolet radiation, arrives at the earth’s outer atmosphere.⏹Ozone in the stratosphere protects life on earth from excessive ultraviolet radiation.⏹The seasons of the earth’s climate results from (1) the 23.30tilt of the earth’s axis of rotation from the normal to the plane of the earth’s orbit around the Sun, (2) the large coverage area of water on the earth (about 75% of the earth’s surface), and (3) the rotation of the earth with associated generation of jet-stream patterns.⏹Radiation passing through the earth’s atmosphere loses most short-wave radiation, butsome arriving at the surface is converted into infrared radiation which is then trapped by water vapor and other tri-atomic molecules in the troposphere and stratosphere, causing global warming.Life on earth is maintained from photosynthesis and conversion of carbon dioxide to oxygen by plants.4.Translate the following parts of sentences in Introduction into proper English.（1）过去对……的研究工作说明……The previous work on … has indicated that…（2）A在1932年做了关于……的早期研究。

高二英语生物学原理与生态现象单选题50题

高二英语生物学原理与生态现象单选题50题1.The function of chlorophyll is to ___.A.absorb sunlightB.produce oxygenC.absorb carbon dioxideD.produce water答案：A。

解析：叶绿素的功能是吸收太阳光进行光合作用。

选项B，产生氧气是光合作用的结果之一但不是叶绿素的主要功能；选项C，吸收二氧化碳的主要结构不是叶绿素；选项D，产生水也是光合作用的结果之一但不是叶绿素的直接功能。

2.Which one is not a characteristic of living things?A.GrowthB.ReproductionC.MovementD.Response to stimuli答案：C。

解析：生物的特征包括生长、繁殖、对刺激作出反应等。

并不是所有生物都能运动，比如植物大多数不能自主运动，所以运动不是生物的普遍特征。

3.The basic unit of life is ___.A.cellB.tissueananism答案：A。

解析：细胞是生命的基本单位。

组织是由细胞组成的，器官是由不同组织构成的，生物体是由多个器官等组成的。

4.What is DNA short for?A.Deoxyribonucleic acidB.Ribonucleic acidC.Deoxyribose acidD.Ribose acid答案：A。

解析：DNA 是脱氧核糖核酸的英文缩写。

选项B 是核糖核酸；选项C 和D 不是正确的缩写。

5.Which process involves the conversion of light energy into chemical energy?A.RespirationB.PhotosynthesisC.DigestionD.Excretion答案：B。

解析：光合作用涉及将光能转化为化学能。

高级英语学术研讨练习50题

高级英语学术研讨练习50题1Advanced English Academic Discussion Exercises 50 Questions Advanced English academic discussion is a significant aspect of language learning that requires a profound understanding of grammar, vocabulary, and language usage in various contexts. The 50 questions presented here aim to comprehensively test and enhance our proficiency in this domain.Firstly, let's consider the accurate application of vocabulary in specific contexts.Take the word "precise" and "accurate" for instance. Although both convey the idea of correctness, they have subtle differences. "Precise" emphasizes exactness and meticulousness, while "accurate" focuses more on being correct and free from errors. Understanding these nuances is crucial in expressing ideas precisely in academic writing.Complex sentence structure analysis is another key area.Sentences like "Despite the challenges he faced, he managed to succeed through sheer determination and hard work." Here, the use of the concessive clause "Despite the challenges he faced" adds depth and complexity to the expression. It showcases the writer's ability to convey amessage in a sophisticated manner.In the realm of grammar, the proper use of tenses is of paramount importance.For example, in historical research papers, past tenses are commonly employed to describe events that have already occurred. However, when presenting general facts or theories that remain valid to date, the present tense is preferred.Moreover, the understanding of pragmatics and semantics plays a vital role.Consider the phrase "I could eat a horse," which is an idiomatic expression meaning extreme hunger and not a literal reference to consuming a large animal.through the analysis and solution of these 50 questions, we can significantly enhance our understanding and mastery of advanced English academic discussion. It allows us to express ourselves precisely, convey complex ideas effectively, and adhere to the norms and standards of academic language. By constantly practicing and reflecting on such exercises, we can improve our language skills and contribute more effectively in the academic arena.2Advanced English Academic Seminar Exercises 50 Questions In the realm of advanced English learning, a set of 50 questions often poses significant challenges and offers valuable learning opportunities. This paper aims to systematically comb and study the advanced English academic knowledge points involved in these 50 questions.The first problem that emerges is the complex grammar structures.Take the use of subjunctive mood as an example. In sentences like "If I were you, I would do it differently," the verb form 'were' is used instead of 'was' to express a hypothetical or contrary-to-fact situation. This kind of grammar point often confuses learners. To understand it thoroughly, we need to analyze numerous examples from authoritative grammar books and real language usage.Another issue is the influence of cultural background on language understanding.Consider idiomatic expressions such as "break a leg" which literally means to have a broken leg but actually means good luck. Without knowing the cultural connotation, it's easy to misunderstand the true meaning. To solve this problem, referring to cultural studies and cross-cultural communication materials is essential.In addition, the semantic ambiguity of some words also poses difficulties.For instance, the word "fine" can mean good, or it can refer to a penalty. To clarify such ambiguity, we need to look at its context in different sentences and explore its multiple meanings.To solve these problems, learners should not only rely on textbooks but also actively engage in extensive reading of original English materials.Online language learning platforms and English-language news websites can provide rich language input. Moreover, participating in language exchange activities and having discussions with native speakers can enhance language perception and cultural understanding.In conclusion, through the analysis and exploration of these 50 questions, we have gained a deeper understanding of advanced English grammar, cultural background, and semantic ambiguity.With continuous learning and practice, we can improve our advanced English proficiency and better apply it in practical communication and academic research.3Advanced English Academic Discussion Exercises: A Critical ReviewThe "Advanced English Academic Discussion Exercises 50 Questions" is a collection that aims to enhance the language proficiency and academic thinking skills of learners. This review will delve into the various aspects of these exercises, including their design rationality, difficulty levels, and coverage scope.The design of these exercises appears to be well-intentioned. They incorporate a diverse range of topics, from literature and history to science and technology, which provides learners with ample opportunities to apply their language skills in different fields. However, upon closer examination, some questions seem rather traditional and lack novelty. In contemporary academia, where interdisciplinary studies are gaining prominence, the exercises could have included more integrated and innovative topics.In terms of difficulty levels, there is a certain imbalance. Some questions are overly simplistic and do not challenge the advanced learners effectively. On the other hand, a few others are so complex that they might overwhelm even the most proficient students. A more gradual and finely tuned difficulty gradient would have been more beneficial, allowing learners to progress smoothly and build confidence at each stage.The coverage scope is broad but not comprehensive enough. While ittouches upon various disciplines, certain key areas such as emerging trends in linguistics and cutting-edge research in cultural studies are conspicuously absent. To keep pace with the evolving academic landscape, it is essential to incorporate the latest developments and hot topics.When comparing with similar questions in different versions of textbooks, it becomes evident that some competing materials offer a more balanced and contemporary selection. They manage to strike a better chord between theoretical knowledge and practical application, making the learning experience more engaging and relevant.In reference to international English academic tests, the 50 questions could draw inspiration from the diverse question types and formats. For instance, including more tasks that require critical analysis, synthesis of multiple sources, and creative thinking would better prepare learners for real-world academic challenges.To improve the exercises, several suggestions can be considered. Firstly, the content should be updated regularly to reflect the latest academic trends and developments. Secondly, the difficulty levels need to be recalibrated for a more seamless learning curve. Additionally, more interactive and collaborative elements could be introduced to encourage active participation and discussion among learners.In conclusion, the "Advanced English Academic Discussion Exercises 50 Questions" has its merits but also leaves room forimprovement. With appropriate enhancements, it has the potential to become a more effective tool for advanced English language learning and academic exploration.。

Study on the mechanism of photosynthesis

Study on the mechanism ofphotosynthesisPhotosynthesis is a process through which plants and other organisms convert light energy into chemical energy in the form of glucose. This process is fundamental for the survival of the plants as it provides them with the necessary energy for growth, metabolism, and reproduction. Understanding the mechanism of photosynthesis is crucial not only for a better comprehension of the complex life processes involved in the plant kingdom but also for developing sustainable and eco-friendly technologies.Photosynthesis takes place in the chloroplasts of plant cells, which are organelles that contain chlorophyll – a pigment that is responsible for the green color of plants. Chlorophyll absorbs solar radiation and transfers the energy to the reaction centers, where it is used to drive the chemical reactions of photosynthesis. The process of photosynthesis can be broadly divided into two stages: the light-dependent reactions and the light-independent reactions.In the light-dependent reactions, which occur in the thylakoid membrane of the chloroplasts, light energy is absorbed by the pigments and used to generate ATP (adenosine triphosphate) and NADPH (nicotinamide adenine dinucleotide phosphate), two compounds that are used in the light-independent reactions. During this stage, water is also split into oxygen and hydrogen ions, which are used to generate a proton gradient necessary for the synthesis of ATP.In the light-independent reactions, which occur in the stroma of the chloroplasts, the energy generated in the light-dependent reactions is used to fix atmospheric carbon dioxide into glucose. This process is known as the Calvin cycle and involves a series of enzymatic reactions that convert carbon dioxide into organic molecules. The Calvin cycle requires ATP and NADPH produced in the light-dependent reactions, as well as other enzymes and cofactors.The process of photosynthesis is regulated by various factors, which can affect its efficiency and rate. Light intensity, temperature, carbon dioxide concentration, and water availability are some of the environmental factors that can affect photosynthesis. In plants, the process is also regulated by feedback mechanisms that respond to changes in the concentrations of ATP and NADPH.The study of the mechanism of photosynthesis is an active area of research, which involves diverse fields such as biochemistry, molecular biology, and biophysics. One of the major challenges in this field is to obtain a detailed understanding of the structure and function of the photosynthetic machinery at the molecular level. Recent advances in structural biology, particularly in X-ray crystallography and cryo-electron microscopy, have provided new insights into the organization and dynamics of the photosynthetic complexes.Another important aspect of the study of photosynthesis is its applications in various fields, such as agriculture, bioenergy, and biotechnology. Understanding the mechanism of photosynthesis can help in the development of improved crops that are more efficient in converting sunlight into biomass, as well as in the development of sustainable and renewable energy technologies based on photosynthetic organisms. Photosynthesis also has potential implications in the fields of medicine and health, as the pigments and compounds involved in the process have been shown to have antioxidant and anti-inflammatory properties.In conclusion, the study of the mechanism of photosynthesis is a complex and multidisciplinary field that has far-reaching implications in diverse fields. The process of photosynthesis is crucial for the survival of plants, the production of food, and the maintenance of the ecosystem. Understanding the intricacies of this process can help in the development of sustainable and eco-friendly technologies, as well as better insights into the fundamental processes of life.。

马来酸桂哌齐特联合腺苷钴胺治疗糖尿病下肢神经病变的临床效果评价

·糖尿病与并发症·糖尿病新世界DIABETES NEW WORLD糖尿病新世界2019年6月[作者简介]张洪波(1979-),男,黑龙江牡丹江人,硕士,副主任医师,研究方向:糖尿病慢性并发症。

糖尿病是临床常见疾病,根据笔者收集的不完全统计的临床相关资料证实,近年来我国糖尿病病发率有上升趋势,而且发病年龄有年轻化趋势[1]。

糖尿病属于代谢性疾病的一种,糖尿病也是终身性疾病的一种,在临床治疗中并无根治的方法,只能通过药物来维持机体平衡[2-3]。

但随着病情的进展,部分患者出现了合并症等情况,例如糖尿病足、糖尿病面部神经病变以及糖尿病下肢神经病变,以糖尿病下肢神经病变为常见的类型[4-5]。

糖尿病下肢神经病变在临床治疗中以药物治疗为主,常用药物为腺苷钴胺,此药物虽然有一定的治疗效果,但不是十分确切。

为了改善此情况,该院以2015年6月—2018年7月收治的30例患者为研究对象,在该次调查中采用了马来酸桂哌齐特联合腺苷钴胺治疗方式,具体情况如下进行详细的阐述,报道如下。

1资料与方法1.1一般资料选取该院糖尿病下肢神经病变治疗的30例患者作为研究,随机的方式分为对照组、实验组,每组15例。

对照组中的男性病例为9例、女性为6例,病例年龄为35~76岁,平均(55.5±1.4)岁。

实验组中的男性病例为10例、女性为5例,病例年龄为36~75岁,平均(55.5±1.5)岁。

两组患者之间的一般资料差异无统计学意义(P >0.05)。

1.2方法对照组给予患者常规治疗,即为控制血糖治疗、腺苷钴胺药物治疗,用法如下:3次/d,2片/次。

DOI:10.16658/ki.1672-4062.2019.12.190马来酸桂哌齐特联合腺苷钴胺治疗糖尿病下肢神经病变的临床效果评价张洪波绥芬河市人民医院,黑龙江绥芬河157399[摘要]目的探讨马来酸桂哌齐特联合腺苷钴胺治疗糖尿病下肢神经病变的临床效果。

金属有机Chapter 9

9HOMOGENEOUS CATALYSISThe catalysis of organic reactions1–4is one of the most important applications of organometallic chemistry and has been a signiﬁcant factor in the rapid devel-opment of the wholeﬁanometallic catalysts have long been used in industrial processes but are now being routinely applied in organic synthetic problems as well.A catalyst is an additive used in substoichiometric amount to bring about a reaction at a temperature below that required for the uncatalyzed thermal reaction.It binds the reactants,or substrates,for the catalytic reaction, causes the desired reaction,and then liberates the reaction products to regenerate the catalyst.The catalyst reenters the catalytic cycle by binding the reagents once more.A typical catalyst may participate in the catalytic cycle101–106times or more,allowing its use in modest or even trace amount.The catalysts we look at are soluble complexes,or homogeneous catalysts,as opposed to catalysts such as palladium on carbon,or heterogeneous catalysts.4These terms are used because the catalyst and substrates for the reaction are in the same phase in the homo-geneous,but not in the heterogeneous,type,where catalysis takes place at the surface of a solid catalyst.Some reactions,such as hydrogenation,are amenable to both types of catalysis,but others are currently limited to one or the other, for example,O2oxidation of ethylene to the epoxide over a heterogeneous silver catalyst or Wacker air oxidation of ethylene to acetaldehyde with homogeneous Pd(II)catalysts.The term homogeneous catalysis also covers simple acid catalysts and non-organometallic catalysis,such as the decomposition of H2O2by Fe2+.Catalytic mechanisms are considerably easier to study in homogeneous systems,where The Organometallic Chemistry of the Transition Metals,Fourth Edition,by Robert H.Crabtree Copyright 2005 John Wiley & Sons, Inc., ISBN 0-471-66256-9235such powerful methods as NMR can be used to both assign structures and follow reaction kinetics.Homogeneous catalysts have the disadvantage that they can be difﬁcult to separate from the product.Sometimes this requires special separation techniques,but in other cases,such as polymer synthesis,the product can be sold with the catalyst still embedded in it.Homogeneous catalysts can also be chemi-cally grafted on to solid supports for greater ease of separation of the catalyst from the reaction products.Although the catalyst is now technically heterogeneous,it often retains the characteristic reactivity pattern that it showed as a homogeneous catalyst,and its properties are usually distinct from those of any of the classical heterogeneous catalysts—these are sometimes called“heterogenized”homoge-neous catalysts.The mechanistic ideas developed in homogeneous catalysis are also becoming more inﬂuential in theﬁeld of classical heterogeneous catalysis by suggesting structures for intermediates and mechanisms for reaction steps.By bringing about a reaction at lower temperature,a catalyst can save energy in commercial applications.It often gives higher selectivity for the desired prod-uct,minimizing product separation problems and avoiding the need to discard the undesired product as waste.The selectivity can be changed by altering the ligands,allowing synthesis of products not formed in the uncatalyzed process. With growing regulatory pressure to synthesize drugs in enantiopure form,asym-metric catalysis has come to the fore,along with enzyme catalysis,as the only practical way to make such products on a large scale.Older commercial processes tended to give side products that had to be discarded,such as inorganic salts. Environmental concerns have promoted the idea of atom economy,which values a process most highly when all the atoms in the reagents are used to form the product,minimizing waste.For example,the Monsanto process of Section12.1 is atom economic because it converts MeOH and CO to MeCOOH with no atoms left over.A typical reaction(Eq.9.1)that is catalyzed by many transition metal com-plexes is the isomerization of allylbenzene(the substrate)into propenylbenzene (the product).Normally,the substrate for the reaction will coordinate to the metal complex that serves as catalyst.The metal then brings about the rearrange-ment,and the product dissociates,leaving the metal fragment free to bind a new molecule of substrate and participate in the catalytic cycle once again.Ph(9.1)9.19.2Before setting out toﬁnd a catalyst for a given reaction,say the one shown in Eq.9.1,theﬁrst consideration is thermodynamic:whether the reaction is favor-able.If the desired reaction were thermodynamically strongly disfavored,as is the conversion of H2O to H2and O2,for example,then no catalyst,however efﬁ-cient,could on its own bring about the reaction.If we wanted to bring about an unfavorable reaction of this sort,we would have to provide the necessary driving force in some way.There are ways of doing this,such as coupling a strongly favorable process to the unfavorable one you want to drive,as Nature commonlydoes with the hydrolysis of ATP(adenosine triphosphate),or we could use the energy of a light photon,as in photosynthesis or we can selectively remove the products(e.g.,by distillation).Normally,the catalyst only increases the rate of a process but does not alter its position of equilibrium,which is decided by the relative thermodynamic stabilities of substrate and products(we discuss ways of getting around this restriction in Section12.4).Fig.9.1a illustrates this point:The substrate S is slightly less stable than the product P,so the reaction will eventually reach an equilibrium favoring P.In the case of9.1going to9.2,the additional conjugation present in9.2is sufﬁcient to ensure that the product is thermodynamically more stable than the starting material and so the reaction is indeed favorable.Normally,the substrate binds to the metal before it undergoes the rearrangement.This substrate–catalyst complex is represented as“M.S”in Fig.9.1.It might be thought that strong binding would be needed.A moment’s reﬂection will show why this is not so.If the binding is too strong,M.S will be too stable,and the activation energy to get to“M.TS”will be just as large as it was in going from S to TS in the uncatalyzed reaction.S cannot bind too weakly because it may otherwise be excluded from the metal and fail to be activated by the metal at all.Similarly,the product P will normally be formed as the complex M.P.Product P must be the least strongly bound of all because if it is not then S will not be able to displace P,and the catalyst will be effectively poisoned by the products of the reaction.Many of these ideas also apply to the chemistry of Nature’s homogeneous catalysts, enzymes.5Each time the complete catalyst cycle occurs,we consider one catalytic turn-over(one mole of product formed per mole of catalyst)to have been completed. The catalytic rate can be conveniently given in terms of the turnover frequency (TOF)measured in turnovers per unit time(often per hour);the lifetime of the catalyst before deactivation is measured in terms of total turnovers.For most transition metal catalysts,the catalyzed pathway is completely changed from the pathway of the uncatalyzed reaction,as shown in Fig.9.1a.Instead of passing by way of the high-energy uncatalyzed transition state TS,the catalyzed reaction normally goes by a multistep mechanism in which the metal stabilizes intermediates that are stable only when bound to the metal.One new transition state M.TS is shown in Fig.9.1.The TS structure in the absence of the metal would be extremely unstable,but the energy of binding is so high that M.TS is now much more favorable than TS and the reaction all passes through the catalyzed route. Different metal species may be able to stabilize other transition states TS —which may lead to entirely different products—hence different catalysts can give different products from the same starting materials.In a stoichiometric reaction,the passage through M.TS would be the slow, or rate-determining,step.In a catalytic reaction the cyclic nature of the system means that the rates of all steps are identical.On a circular track,on average the same number of trains must pass each point per unit time.The slow step in a catalytic process is called the turnover limiting step.Any change that lowers the barrier for this step will increase the turnover frequency(TOF).Changes inM[M.S][M.P][M.I]irreversible catalyst deactivation product[M ′′]substrate (b )off-loop species[M.S ′]intermediate active catalyst catalyst precursorM ′(a )FIGURE 9.1(a )A catalyst lowers the activation energy for a chemical reaction.Here the uncatalyzed conversion of substrate S to product P passes by way of the high-energy transition state TS.In this case the metal-catalyzed version goes via a different transition state TS ,which is very unstable in the free state but becomes viable on binding to the catalyst as M.TS .The arrow represents the M −TS binding energy.The uncatalyzed and catalyzed processes do not necessarily lead to the same product as is the case here.(b )Typical catalytic cycle in schematic form.other barriers will not affect the TOF.For a high TOF,we require that none of the intermediates be bound too strongly (otherwise they may be too stable and not react further)and that none of the transition states be prohibitively high in energy.Indeed,the whole reaction proﬁle must not stray from a rather narrowALKENE ISOMERIZATION239 range of free energies,accessible at the reaction temperature.Even if all this is arranged,a catalyst may undergo a catalytic cycle only a few times and then“die.”This happens if undesired deactivation reactions are faster than the productive reactions of the catalytic cycle itself.There are many ways in which a catalyst can fail,and for success it is often necessary to look hard for the right metal,ligand set,solvent,temperature range,and other conditions.Many of the reactions that occupied the attention of the early workers were relatively forgiving in terms of the range of possible catalysts and conditions.Some of the problems that are under study today,notably alkane conversions,constitute more searching tests of the efﬁciency of homogeneous catalysts.Figure9.1b shows a schematic catalytic cycle.The active catalyst M is often rather unstable and is only formed in situ from the catalyst precursor(or precat-alyst),M .If during the reaction we observe the system,for example,by NMR, we normally see only the disappearance of S and the appearance of P.Decreasing the substrate concentration[S]and increasing the metal concentration[M]may allow us to see the complex.We may still see only M because only a small fraction of the metal is likely to be on the loop at any given time.Even if an observed species appears to be an intermediate,we still cannot be sure it is not M·S ,an off-loop species.If a species builds up steadily during the reaction, it might be a catalyst deactivation product M ,in which case the catalytic rate will fall as[M ]rises.Excellent reviews are available on the determination of mechanism in catalytic reactions.39.1ALKENE ISOMERIZATIONMany transition metal complexes are capable of catalyzing the1,3-migration of hydrogen substituents in alkenes,a reaction that has the net effect of moving the C=C group along the chain of the molecule(e.g.,Eq.9.1).This is often a side reaction in other types of catalytic alkene reaction,desired or not according to circumstances.Two mechanisms are most commonly found:theﬁrst goes via alkyl intermediates(Fig.9.2a);the second,byη3-allyls(Fig.9.2b).Note that in each cycle,all the steps are reversible,so that the substrates and products are in equilibrium,and therefore although a nonthermodynamic ratio of alkenes can be formed at early reaction times,the thermodynamic ratio is eventually formed if the catalyst remains active long enough.In other catalytic reactions,we sometimesﬁnd that the last step is irreversible.As we shall see later,this distinction has important practical consequences in allowing the formation of grossly nonthermodynamic ratios(e.g.,in asymmetric catalysis).Alkyl MechanismIn the alkyl route,we require an M−H bond and a vacant site.The alkene binds and undergoes insertion to give the alkyl.For1-butene,the alkyl might be the1◦or the2◦one,according to the regiochemistry of the insertion.If the1◦alkyl is240HOMOGENEOUS CATALYSIS((FIGURE 9.2The (a )alkyl and (b )allyl mechanisms of alkene isomerization.The open box represents a 2e vacancy or potential vacancy in the form of a labile 2e ligand.formed,βelimination can give back only 1-butene,but βelimination in the 2◦alkyl,often faster,can give both 1-and cis -and trans -2-butene.Since insertion to give the 1◦alkyl is favored for many catalysts,nonproductive cycling of the 1-butene back to 1-butene is common,and productive isomerization may be slower.The initial cis/trans ratio in the 2-butenes formed depends on the catalyst;the cis isomer is often favored.The ﬁnal ratio depends only on the thermodynamics,and the trans isomer is preferred.A typical isomerization catalyst is RhH(CO)L 3(L =PPh 3).6As this is a coordinatively saturated 18e species it must lose a ligand,PPh 3in this case,to form a coordinatively unsaturated intermediate (<18e),able to bind the alkene.ALKENE HYDROGENATION241 Allyl MechanismThe second common mechanism involves allyl intermediates and is adopted by those metal fragments that have two2e vacant sites but no hydrides.It has been established for the case of Fe3(CO)12as catalyst,a system in which“Fe(CO)3,”formed by fragmentation of the cluster on heating,is believed to be the active species.7The cluster itself is an example of a catalyst precursor.As a14e species, Fe(CO)3may not have an independent existence in solution,but may always be tied up with substrate or product.The open square in Fig.9.2represents a vacant site or a labile ligand.In this mechanism the C−H bond at the acti-vated allylic position of the alkene undergoes an oxidative addition to the metal. The product is anη3-allyl hydride.Now,we only need a reductive elimina-tion to give back the alkene.Again,we can have nonproductive cycling if the H returns to the same site it left,rather than to the opposite end of the allyl group.An experimental distinction7can be made between the two routes with a crossover experiment(Section6.5)using the mixture of C5and C7alkenes of Eq.9.2.For the allyl mechanism,we expect the D in9.3a to end up only in the corresponding product9.3b having undergone an intramolecular1,3shift.For the hydride mechanism,the D will be transferred to the catalyst that can in turn transfer it by crossover to the C5product.DFe(CO)D ++9.3a9.3b(9.2)žCatalytic cycles involve a series of reaction steps of the types seen inChapters5–8.žThe catalyst precursor is usually transformed in some way before enteringthe cycle.žObservable species in the catalytic solution are often off-loop species(Fig9.1).9.2ALKENE HYDROGENATIONHydrogenation catalysts3add molecular hydrogen to the C=C group of an alkene to give an alkane.Three general types have been distinguished,according to242HOMOGENEOUS CATALYSIS the way each type activates H 2.This can happen by (1)oxidative addition,(2)heterolytic activation,and (3)homolytic activation.Oxidative AdditionPerhaps the most important group employs oxidative addition,of which RhCl (PPh 3)3(9.4,Wilkinson’s catalyst)is the best known.A catalytic cycle that is important under certain conditions is shown in Fig.9.3.Hydrogen addition to give a dihydride leads to labilization of one of the PPh 3ligands (high trans effect of H)to give a site at which the alkene binds.The alkene inserts,as in isomerization,but the intermediate alkyl is irre-versibly trapped by reductive elimination with the second hydride to give an alkane.This is an idealized mechanism.3In fact,9.4can also lose PPh 3to give RhCl (PPh 3)2,and dimerize via halide bridges and each of these species have their own separate catalytic cycles 3c that can be important under different condi-tions.Indeed,RhClL 2reacts so much faster with H 2than does RhClL 3that the vast majority of the catalytic reaction goes through RhClL 2under most condi-tions.By reversibility arguments,the more rapid oxidative addition of H 2to the 3-coordinate d 8RhClL 2to give 5-coordinate d 6RhH 2ClL 2relative to the corre-sponding 4-coordinate →6-coordinate conversion is consistent with the tendency for faster reductive elimination from 5-coordinate d 6species that was discussed in Section 6.5.In a key study by Tolman and co-workers 3d ,the dihydride was directly seen by 31P NMR under H 2and the reversible loss of the PPh 3trans to a hydride detected from a broadening of the appropriate resonance,as discussed in Section 10.5.Figure 9.3represents the hydride mechanism in which H 2adds before the oleﬁn.Sometimes the oleﬁn adds ﬁrst (the oleﬁn mechanism )as is found for [Rh(dpe)(MeOH)2]BF 4.3eRhCl L L H HL Rh ClL L H RhCl L L HLH Rh Cl L H FIGURE 9.3Mechanism for the hydrogenation of alkenes by Wilkinson’s catalyst.Other pathways also operate in this system,however.ALKENE HYDROGENATION243PPh3Cl Rh PPh3PPh39.4Since we need to bind two hydrides and the alkene,for a total electron count of4e,the16e catalyst RhCl(PPh3)3needs to dissociate a ligand,PPh3in this case,to do this.The PEt3analog of9.4reacts with H2to give a stable and cat-alytically inactive dihydride RhH2Cl(PEt3)3,9.5.The smaller PEt3ligand does not dissociate and so9.5is not an active catalyst.All we have to do to make the PEt3analog active is artiﬁcially arrange to generate the desired RhH2ClL2 intermediate by forming it in situ by starting with0.5equiv of[(nbd)Rh(µ-Cl)]2 and adding2equiv of PEt3,for aﬁnal P/Rh ratio of2.Under H2,the norbor-nadiene(nbd)is removed by hydrogenation,and we get RhH2Cl(PEt3)2,which is an active hydrogenation catalyst under these conditions.8A key prerequisite for catalysis in many systems is coordinative unsaturation,that is,an open site at the metal.HPEt3H Rh PEt3PEt39.5As predicted by the mechanism of Fig.9.3,the hydrogen gives syn addition to the alkene,although it is possible to tell only this in certain cases.For example,DD(9.3)33DIsomerization is often a minor pathway in a hydrogenation catalyst because the intermediate alkyl mayβ-eliminate before it has a chance to reductively eliminate. The more desirable catalysts,such as9.4,tend to give little isomerization.The selectivity for different alkenes(the hydrogenation rates change in the following order:monosubstituted>disubstituted>trisubstituted>tetrasubstituted=0)is determined by how easily they can bind to the metal;the poorer ligands among them are reduced slowly,if at all.This means that9.4reduces the triene9.6 largely to the octalin9.7(Eq.9.4).Heterogeneous catalysts give none of this product,but only the fully saturated decalin(9.9),and the isomerization product, tetralin(9.8)(Eq.9.4).The C=O and C=N double bonds of ketones and imines are successfully reduced only by certain catalysts.Other functional groups that244HOMOGENEOUS CATALYSIS can be reduced by heterogeneous catalysts,such as−CN,−NO2,−Ph,and −CO2Me are not reduced by the usual homogeneous catalysts.2339.99.89.7isomerizationproduct (minor)hydrogenation product(major)+9.6(9.4)IrCl(PPh3)3,the iridium analog of9.4,is inactive because of the failure of the dihydride IrH2Cl(PPh3)3to lose phosphine;this is a result of the stronger metal–ligand bond strengths usually found for the third-row ing the same general strategy we saw for Rh,[(cod)Ir(µ-Cl)]2is active if only2mol of phosphine are added per metal.A more useful catalyst is obtained by replacing the chloride with a“noncoordinating”anion and changing the ligands to give the precursors[(cod)Ir(PMePh2)2]+PF6−,9.10,and[(cod)Ir(py)(PCy3)]+PF6−, 9.11.8These catalysts tend to bind a solvent,such as EtOH,much moreﬁrmly than do such uncharged catalysts as9.4,for example,to give the isolable species [IrH2(solv)2(PMePh2)2]+PF6−(solv=acetone,ethanol,or water).This results from the presence of hydrides and the net cationic charge,which tend to make the metal a harder Lewis acid.Unlike many noncationic catalysts,these species are also air stable and even tolerate halocarbons.As a result,the catalyst can be used in CH2Cl2,a much more weakly coordinating solvent than pound 9.11has the unusual feature that it can reduce even highly hindered alkenes such as Me2C=CMe2.This is probably because these alkenes do not have to compete with dissociated phosphine or a coordinating solvent for a site on the metal,and perhaps also because the{Ir(py)(PCy3)}+fragment is not very bulky.The high activity of9.10atﬁrst escaped attention because it was initially tested in EtOH, which at that time was the conventional solvent6for hydrogenation.Screening a new catalyst under a variety of conditions is therefore advisable.9.119.10+Ir PMe2PhPMe2Ph+IrPCy3pyDirecting EffectsThe catalyst 9.11shows strong directing effects,which can be very useful in organic synthetic applications (see Section 14.2).9This means that H 2is added to one face of the substrate,if there is a coordinating group (e.g.,−OH,−COMe,−OMe)on that face (Eq.9.5).The net positive ionic charge makes the metal hard enough to bind to the directing group and,as IrL 2+is a 12e fragment,it still has enough vacant sites left to bind both H 2and the alkene to give the key intermediate 9.12.Of the four possible geometrical isomers of the saturated ketone,only one is formed,H 2having been added cis to the directing group.OO HH3(9.5)Asymmetric CatalysisThe corresponding “RhL 2+”catalysts were developed by Schrock and Osborn.10a Their most important application is asymmetric catalysis.10b Equation 9.6shows how the achiral alkene 9.13can give two enantiomers 9.14and 9.15on hydro-genation.RCCH 2R ′R C CH 3R ′H R C CH 3R ′H 9.159.149.13+(9.6)Any alkene having this property is called prochiral ,which implies that the two faces of the molecule are different.In 9.13,one face has a clockwise arrangement of R,R ,and =CH 2about the central carbon;the other face has an anticlockwise arrangement of these groups.If the H 2is added from one face,one enantiomer is formed;if from the other face,the other enantiomer is the product.If we were to bias the addition of H 2to one face,then we would have an asymmetric synthesis.As shown in Eq.9.7,when a prochiral alkene binds to an achiral metal,two enantiomers are formed;that is,the complex is chiral even though neitherthe ligand nor the metal were chiral before the complex was formed.One way of thinking about this is to regard the carbon indicated by the asterisk as having four different substituents,one of which is the metal.RC CH2 R′RC CH2R′RC CH2R′ML nML n**9.179.16enantiomers+(9.7)RC CH2 R′RC CH2R′RC CH2R′MLML n**diastereomers+9.189.19**n*(9.8)The key point is that if the ML n catalyst fragment can also be made chiral (say because a ligand L has an asymmetric carbon),then we can use one resolved enantiomer of the chiral complex as catalyst.In Eq.9.8,instead of forming two enantiomeric complexes such as9.16and9.17,which react at equal rates to give achiral products,we will have diastereomeric alkene–catalyst complexes, 9.18and9.19,because we now have two asymmetric centers present,C∗in the coordinated alkene and the asymmetric ML∗n fragment.Since diastereomers gen-erally have different chemical properties,9.18and9.19normally have different rates of hydrogenation.This bias on the rates of hydrogenation can selectively give us one of the pair of enantiomers9.14or9.15over the other.In summary, one enantiomer of the catalyst should preferentially give one enantiomer of the hydrogenated alkene,and the other enantiomer give the other product.This is an extremely valuable method because we can obtain a large amount of one enan-tiomeric product from a small amount of resolved material(the catalyst).This is precisely the method Nature uses to make pure enantiomers;enzymes are such efﬁcient asymmetric catalysts that essentially only one enantiomer is normally formed in most enzymatic processes.In asymmetric hydrogenation,95–99%enantiomeric excess[e.e.=100×{amount of major isomer−amount of minor isomer}/{total of both isomers}] can be obtained in favorable cases.Theﬁrst alkenes to be reduced with high asymmetric induction contained a coordinating group,examples of which are shown as9.20and9.21.PhNHCOMeCO2MeNHCOMeCO2Me9.219.20These are believed to bind to the metal via the amide carbonyl just as we saw hap-pen in directed hydrogenation.This improves the rigidity of the alkene–catalyst complex,which in turn increases the chiral discrimination of the system.As in directed hydrogenation,a12e catalyst fragment,such as that formed from the Schrock–Osborn catalyst,is required.One of the best ways of making the metal chiral is to use the ligand shown as9.22,called BINAP.This ligand has a so-called C2axis;this simply means that it has the symmetry of a helical bolt,which can,of course,either have a left-handed or a right-handed thread.The chiral centers impose a twist on the conformation of the BINAP-metal complex,which in turn leads to a chiral, propeller-like arrangement of the phenyl groups on phosphorus(9.23).These phenyl groups can be thought of as transmitting the chiral information from the asymmetric centers to the binding site for the alkene.The advantage of a C2 symmetry is that the substrate sees the same chirality however it binds;we can think of the substrate as being analogous to a nut with a left-hand thread that will mate with a left-handed(but not a right-handed)bolt,whichever face of the nut is tried.2C2 axis2P PM9.23In the simplest case,one face of the substrate binds better to the catalyst than does the other.Let us say that,if H2were added to this face,we would get the S hydrogenation product.It was once thought that this preferential binding of the substrate always determines the sense of asymmetric induction.Halpern andco-workers 11showed that in a system that gives the R product in good yield,the metal is bound to the “wrong”face in the major diastereomer (9.24),the face that would be expected to give the S product,and so it is the minor isomer of the catalyst–alkene complex that gives rise to most of the product.This in turn means that the minor isomer must react at about 103times the rate of the major isomer (Eq.9.9).Since 9.24and 9.25interconvert rapidly,9.24is continually converting into 9.25because the faster hydrogenation of 9.25continually depletes L n M *L n M *HHL n M *RR ′R ′R RR ′RR ′H R ′R H9.25minor 9.24majorR -product minor S -product major(9.9)the concentration of this minor isomer.Note that Eq.9.9is an example of the “oleﬁn mechanism.”Asymmetric alkene hydrogenation was used in the successful commercial pro-duction of the Parkinson’s disease drug L -DOPA by hydrogenation of the alkene9.26and of the pain reliever,naproxen.12aNHCOMeCO 2MeMeOAcO9.26Another commercial success,this time for Ciba–Geigy,now Novartis,has been the synthesis of the herbicide,(S )-metolachlor,from the imine shown below using an iridium catalyst.The key advantage of iridium is the extremely impres-sive rate (>200,000turnovers h −1)and catalyst lifetime (∼106turnovers)at the。

小学上册U卷英语第4单元测验试卷

小学上册英语第4单元测验试卷英语试题一、综合题(本题有100小题，每小题1分，共100分.每小题不选、错误，均不给分)1.What do you call the person who repairs buildings?A. ArchitectB. BuilderC. ContractorD. Engineer2. A ______ (生态系统) thrives on plant life.3.The chemical symbol for gallium is ______.4.Which word means "to run fast"?A. WalkB. JogC. SprintD. Stroll5.The ______ (小鸟) chirps cheerfully in the ______ (早晨).6.What is the name of the famous artist known for his portraits?A. Vincent van GoghB. Leonardo da VinciC. Pablo PicassoD. Claude Monet7.I can create my own characters with my ________ (玩具名称).8.She is ___ the piano. (playing)9.My ________ (玩具名称) is an essential part of my life.10.There are _______ (three/four) apples on the table.11.I think it's polite to call people ____. (我认为称呼人们为____是礼貌的。

)12.I like to ______ (参加) motivational workshops.13.The __________ (历史的回响) lingers in consciousness.14.How many seasons are there in a year?A. 2B. 3C. 4D. 5C15.The chemical formula for iodine monochloride is _______.16.What is the largest organ in the human body?A. HeartB. LiverC. SkinD. BrainC17.Respiration is a process that occurs in ________.18.The park is ________ my house.19.What do you call a person who studies plants?A. BotanistB. ZoologistC. BiologistD. Ecologist20.The chemical symbol for selenium is ______.21. A _______ reaction is when energy is absorbed.22.The _______ (金鱼) can come in various colors.23. A _______ is a type of reaction that produces a precipitate.24.The teacher is _____ the students. (helping)25. A ________ (气候带) refers to the climate of an area.26.The ________ (环境修复) is crucial for sustainability.27. A ____(feedback mechanism) collects opinions and suggestions.28.What do you call a story from the past?A. FictionB. MythC. HistoryD. NovelC29.What do you call a young chicken?A. DucklingB. ChickC. CalfD. KidB30.Many _______ can be used for making crafts.31.My sister is a ______. She enjoys helping animals.32.The fire is _______ (warm).33.An electrolyte is a substance that conducts electricity when _____.34.The grass is ________ and green.35. A goldfish can be kept as a ______ (宠物).36.My _______ (狗) loves to dig in the yard.37. A ______ is a type of energy measured in joules.38.What do we call the part of the plant that grows underground?A. LeafB. StemC. RootD. FlowerC39.What is the capital of the Dominican Republic?A. Santo DomingoB. SantiagoC. Puerto PlataD. La RomanaA40.What is the name of the celestial event when the Earth passes between the sun and the moon?A. Lunar EclipseB. Solar EclipseC. Total EclipseD. Partial Eclipse41.Which fruit is red and often eaten in pies?A. BananaB. GrapeC. AppleD. Orange42.My brother is always full of __________ (活力).43.What do we call the smallest unit of life?A. OrganB. CellC. TissueD. OrganismB Cell44.ssance was a period of renewed interest in __________. (艺术与科学) The Rena45.What is the largest mammal in the world?A. ElephantB. Blue WhaleC. GiraffeD. HippopotamusB46.The ______ helps students prepare for exams.47.She is ______ her homework quickly. (finishing)48. A ____ is a tiny animal that loves to hop around in gardens.49. A compound is made up of two or more ______ elements.50.What is the main organ of the human body that pumps blood?A. BrainB. HeartC. LiverD. KidneyB51.The cat is __________ on the sofa.52.What is the term for the distance light travels in one year?A. Light-YearB. Astronomical UnitC. ParsecsD. Cosmic Yard53.We like to sing ________ songs.54.小狼) plays with its siblings. The ___55.The ________ sings beautifully in the morning.56.What is the value of 10 2 × 3 + 1?A. 5B. 6C. 7D. 8C57.The ancient Greeks made significant advances in ________ (建筑).58.The main component of the air we breathe is ______.59.My friend loves __________ (探索新的领域).60.The panda's diet is mostly ________________ (竹子).61.What is the term for a baby goat?A. CalfB. LambC. KidD. FoalC62.Insects can harm __________ (植物).63.What do you call a shape with six sides?A. TriangleB. SquareC. HexagonD. Pentagon64.ahal was built as a ________ (陵墓). The Taj65.In which country is the Eiffel Tower located?A. ItalyB. GermanyC. FranceD. Spain66.The city of Port Moresby is the capital of _______.67.We are going to _____ a picnic. (have)68.The ______ helps us understand technology better.69.The _______ is essential for pollination.70.What is the name of the famous clock tower in London?A. Elizabeth TowerB. Big BenC. Tower BridgeD. London BridgeB71.The dog loves to ______ (run) in the yard.72.The __________ is refreshing after a hot day. (凉爽的晚风)73.I have a _____ (手链) that I made with colorful beads. 我有一个用彩色珠子制作的手链。

小学上册第九次英语第五单元测验卷(有答案)

小学上册英语第五单元测验卷(有答案)英语试题一、综合题(本题有50小题，每小题1分，共100分.每小题不选、错误，均不给分)1 What do we call the time of year when plants bloom?A. WinterB. SpringC. SummerD. Fall2 We had a fun picnic with our toy ____. (玩具名称)3 I found a ________ under the leaf.4 A magnet has a north and a ______ pole.5 My friend can ________ well.6 The ______ (马) has a mane that flows in the wind.7 My brother enjoys playing __________. (电子游戏)8 The main gas produced by burning fossil fuels is _______.9 Every Friday, we have a ________ (运动会) at school. I participate in the ________ (跑步) race.10 The ________ was a key battle in the Revolutionary War.11 What is the name of the large body of saltwater?A. LakeB. RiverC. Ocean答案:C12 Recognizing plant ______ can help you manage your garden effectively. (识别植物的需求可以帮助你有效管理花园。

)13 What is 12 + 12?A. 22B. 24C. 26D. 2814 My friend, ______ (我的朋友), is a great storyteller.15 The chemical formula for ammonium nitrate is ______.16 Many _______ have interesting facts and histories.17 A solute is the substance that is ______ in a solution.18 I have a toy ________ (玩具名称) that sings songs.19 My dad loves to teach me about __________ (科学).20 My favorite fruit to eat is ______.21 Sulfuric acid is a common industrial ________.22 The capital of Kazakhstan is __________.23 The _____ (小羊) loves to be close to its mother.24 My cousin has a pet ____ (fish) in a tank.25 The __________ is a region known for its local produce.26 What do we call a building where we go to pray?A. ChurchB. SchoolC. Museum27 The first modern democracy was established in ________ (雅典).28 What is the name of the first artificial satellite launched into orbit?A. Explorer 1B. Vanguard 1C. Luna 1D. Sputnik 129 The goat has curved ______ (角).30 Heat can speed up ________ reactions.31 She has a nice ___. (voice)32 ts can survive in _____ (干燥) conditions. Some pla33 I enjoy gardening and planting ______ (花) and vegetables.34 What is the temperature of ice?A. 0 degrees CelsiusB. 32 degrees FahrenheitC. Both A and BD. 100 degrees Celsius答案:C35 The ____ has a unique pattern and runs fast.36 The _____ (橡树) is very strong.37 What is the term for the process of water vapor turning into liquid water?A. EvaporationB. CondensationC. PrecipitationD. Sublimation38 Which instrument has keys and makes music?A. GuitarB. DrumC. PianoD. Flute答案:C39 A chemical equation shows the _____ of a chemical reaction.40 The tortoise is slow but very _______ (坚韧).41 What is the name of the tree that produces acorns?A. PineB. MapleC. OakD. Birch答案:C42 A _______ can be a beautiful centerpiece for a table.43 What do we call the study of the distribution and movement of populations?a. Demographyb. Sociologyc. Anthropologyd. Geography答案:a44 What do you call a book of maps?A. DictionaryB. AtlasD. Encyclopedia45 A dog can _______ very loudly.46 The starfish can regenerate lost ______ (部分).47 What is 10 - 7?A. 1B. 2C. 3D. 448 What is the opposite of big?A. SmallB. TallC. HugeD. Large答案:A49 A reaction that produces a gas is indicative of a ______ change.50 A ______ (生态系统服务) is crucial for human well-being.51 My cousin is a ______. She has many pets.52 The _____ (冰淇淋) is cold.53 War was a period of political tension between the __________ and the USSR. (美国) The Cold54 A _____ is a long, narrow inlet of the sea.55 The __________ is known for its ancient ruins. (希腊)56 I like to go ______ (滑雪) in the mountains during winter.57 The smallest particle of an element is an ______.58 Which holiday comes in December?A. HalloweenB. ThanksgivingC. ChristmasD. Easter59 Chemical reactions can be classified as _____ (synthesis, decomposition, single replacement, double replacement).60 The fish has colorful _________. (鳞片)61 A __________ is a mixture that contains particles large enough to see and separate.62 My sister is my best _______ because we share everything.63 What do we call the study of living organisms?A. BiologyB. ChemistryC. PhysicsD. Geology64 I feel excited when I __________ because it makes me __________.65 Minerals are natural substances that make up ______ and rocks.66 The movement of water can reshape the ______.67 The __________ (历史的意义) can evolve over time.68 The __________ (历史的声响) echoes through time.69 I saw a _____ (豹子) at the wildlife sanctuary.70 The capital of Zimbabwe is __________.71 The _____ (cactus) grows in the desert.72 A __________ is a large area of flat land that is higher than the surrounding area.73 My favorite _____ is a cuddly lion.74 What do you call it when water falls from the sky?A. RainB. SnowC. HailD. Sleet答案:A75 My mom is ______ (cooking) dinner.76 A _____ is a phenomenon where the moon blocks the sun.77 The __________ is a well-known city for its cuisine.78 The bird builds a ______.79 The ______ (草丛) is home to many critters.80 Elements on the left side of the periodic table are usually __________ (金属).81 What do we call a young dolphin?A. CalfB. PupC. KidD. Foal82 I like to play ___ (piano) after dinner.83 His favorite sport is ________.84 A mouse is a common ______ (宠物).85 The __________ (台风) caused heavy rain last year.86 The study of Earth's geology is essential for understanding ______ resources.87 The ice cream is ______ (melting) in the heat.88 Kinetic energy is the energy of ______.89 A crab can be found on the _______ (海滩).90 Which insect is known for its ability to make honey?A. AntB. BeeC. FlyD. Mosquito答案:B91 The playground is ___. (fun)92 The _____ (雨伞) is colorful.93 How many letters are there in the English alphabet?A. 24B. 25C. 26D. 27答案:C94 What do we call the act of drawing a conclusion based on evidence?A. InferenceB. InductionC. DeductionD. Analysis答案:A95 I have a _____ (电子玩具) that lights up.96 My ________ (玩具名称) is a great tool for expressing myself.97 What color are strawberries?A. BlueB. RedC. YellowD. Green答案:B98 The kids are playing ___ the yard. (in)99 What do we call the study of insects?A. EntomologyB. ZoologyC. BotanyD. Ecology答案: A100 Every morning, I say ______ (早安) to my family and wish them a great day. It spreads ______ (快乐).。