文献综述 2B
二语习得文献综述

Chapter ⅠIntroduction of Attention1.1 What is Attention?The word attention in dictionary is defined as the action of applying one’s mind to something or somebody or noticing something or somebody, a kind of particular care. As an important concept in psychology, attention refers to the cognitive process of selectively concentrating on one thing while deliberately ignore other things. Among the various cognitive process in human mind, attention is usually considered as the most important. A leading psychologist William James gave us a clear definition: “everyone knows what attention is. It is the taking possession by the mind in clear and vivid form, of one out of what seem several simultaneously possible objects or trains of thought…it implies withdraw from something in order to deal effectively with others.( William James. 1890)Today, rather than regarding attention as a filter on input most psychologists now conceptualize it as a mechanism of cognitive processing and more specifically another instance of construction:depending on what stimulus they wish to pay attention to, people select certain pieces of information from among those they receive and construct a perception from them.The first and most basic characteristic of the mind is that it can only focus effectively on one thing at a time and can only focus on the selected goal for a short period of time before it shifted to something else.Thus, the processing capacity is limited. But sometimes the amount of new information being attended to depend on how many cognitive processing resources is needed for each stimulus. If you are confronted with a demanding task,full attention is required to accomplish it .However, if you are doing habitual or automatic routine, you may split your attention to other activities.Therefore,it is safe to say that human cannot attend to two demanding tasks at the same time.Therefore, people should select information for processing according to priority.The second characteristic is that human mind is always occupied by a continual stream of thoughts and considerations without any rest. Therefore, focusing on one thing is realized by subjectively choosing a goal to attend to at a certain period of time, not just by blocking out distractions.1.2 Vocabulary Knowledge and Vocabulary Acquisition ProcessNo doubt, foreign language vocabulary is viewed as a footstone factor in successful communication (Ellis 1994)and,to a great extent,in high-level reading ability and comprehension. A large number of the studies in SLA examine the role of context in vocabulary acquisition which takes place through reading or reading-associated tasks.Context plays a primordial role in this acquisition by supplying the necessary input and trigger.A plausible explanation of lexical acquisition is a theory about the active role of the learner in the process of vocabulary acquisition.Learners should be encouraged to make their own lexical associations when they are actively learning new vocabulary.The importance of vocabulary knowledge in L2 learning is supported by the schema-based approach to language learning.The learning theory based on information processing and the role of cognitive processes suggests that the information from long-term memory can be used to enrich the learners’understanding or retention of the new ideas by providing related information or schemata into which the new ideas call be organized.An often quoted definition of learning is the process by which information is obtained,stored,retrieved and used.Learning in itself cannot be separated from what is being learned or from the process of learning.For the learning of L2 vocabulary, Brown(1993)has identified five steps:(a)having sources for encountering new words;(b)getting a clear image,either visual or auditory or both, of the forms of the new words;(c)learning the meaning of the words;(d)making a strong memory connection between the forms and the meanings of the words;(c)using the words.Accordingly, learning L2 vocabulary is,to some extent,related to these five steps,which,in a more or less degree,is associated with the attention mechanism in the cognitive process of L2 lexical acquisition. Lexical knowledge lies at the core of L2 vocabulary acquisition but as Laufer observe,“no clear and unequivocal consensus exists as to the nature of lexical knowledge”.According to Nation (2004) vocabulary learning process consists of three psychological conditions:noticing,retrieval and creative use.Noticing,the first process is induced by, forexample,the salience of the word,learners’attention to the word,learner’s interest and motivation,etc.Noticing involves decontextualization and negotiation.The second process,retrieval is the proper way to strengthen the memory and the creative or generative use makes evident the extent to which the language user demonstrates his ability to use knowledge of linguistic rules for communication.Chapter ⅡAttention in Noticing HypothesisSchmidt raises his claim that noticing is the necessary and sufficient condition for the conversion of input into intake for learning (1994). Awareness of the form is a prerequisite for the learning of a form. In the light of Schmidt, noticing is in need of learner’s focal attention and awareness, and subliminal learning cannot explain SLA process. The noticing hypothesis further states that it is whatever features of the input relevant for the target system not just the input in a global sense that must be noticed. From the above theory, we can see that only by attention to specific aspects of the input can learners acquire these aspects of the input.According to Schmidt, by noticing is meant the subjective experience of the stimuli. It seems that noticing critically contains awareness, and Schmidt appears to include awareness with attention as central to noticing, Schmidt also expounds the role and the nature of noticing. In a restrict sense, noticing is isomorphic with Tomlin and Villa’s (1994) detection of selective attention, and to Robinson’s detection plus rehearsal in short term memory. Schmidt assumed that the objects of attention and noticing are elements of the surface structure of input language, rather than any abstract rules or principles of which such instances may be examples. Schmidt made relative claim that unattended stimuli remain in immediate short term memory for a very short time, and attention is the necessary and sufficient condition for stimuli to enter long term memory. In SLA, it is usually considered that attention selects the essential materials in input to be accessible for further central mental processing.Although consensus has arrived on the importance of attention, disagreement exists in the amount and types of attention. In Tomlin and Villa’s view (1994), attention contains three interrelated networks, namely, alertness, orientation, and detection, with alertness and orientation serving to make detection more likely, however, not ensuring detection or learning, and detection being the process by which particular examples are registered in memory and therefore can be made accessible to whatever the key processes are for learning (Tomlin & Villa, 1994).According to them, detection requires no awareness. Up to this point, further mention should be made of awareness under the framework of both SLA and cognitive science. Awareness refers to a particular state of mind in which an individual has undergone a specific subjective experience of some cognitive content or external stimulus.For the two opposing views of attention by Schmidt and Tomlin & Villa, Robinson has attempt to compromise their views. Noticing is defined as what is detected and then further activated following the allocation of attention resources from a central executive. (Robinson, 1995). Robinson argues that different tasks may result in different cognitive processing, and that different task demands may have an effect on attentional allocation, which consequently works on the quality of second language comprehension and production. Robinson argues that both Tomlin & Villa’s detection and Schmidt’s noticing require attention, and learning won’t occur without attention. Robinson persists that awareness is crucial to noticing, agreeing with Schmidt claim that there is no learning without awareness at the level of noticing.Schmidt and Robinson have conviction that awareness is necessary for learning. In terms of his strong version of noticing hypothesis, while there is evidence for subliminal perception, subliminal learning is impossible. Unattended stimuli enter short term memory. If they are not noticed and selected via attention, they are not likely to enter long term memory. Therefore, as claimed by Schmidt (1990), only conscious noticing causes intake, which is meant to be pertinent to the learning of all respects of language. Schmidt still argued that the amount of noticing is in proper proportion to that of learning in that whoever notices most means whoever pays attention most. What’s more, Schmidt claims that many factors such as task demands, frequency, ect. Noticing is not end of the learning process but the initial step in language building.Schmidt (1990) identifies three aspects of consciousness involved in language learning: awareness, intention and knowledge. The first sense, consciousness as awareness, embraces noticing. According to Schmidt (1995), "the noticing hypothesis states that what learners notice in input is what becomes intake for learning." Schmidt also states that a) whether a learner deliberately attends to a linguistic form in the input or it is noticed purely unintentionally, if it is noticed it becomes intake; and b) that noticing is a necessary condition for SLA. To help clarify Schmidt's hypothesis and the place of noticing in SLA the following model, proposed by Ellis, is useful.Ellis has based his model on current theories of SLA, where two main stages are seen to be involved in the process of input becoming implicit knowledge. The first stage, in which input becomes intake, involves learners noticing language features in the input, absorbing them intotheir short-term memories and comparing them to features produced as output. With regard to short-term memory, Kihlstrom (1984) suggests that 1) consciousness and short-term memory are essentially the same; 2) that for language items to be stored in long-term memory they must be processed in short-term memory; and 3) that items not processed into short-term memory or not further encoded into long-term memory from short-term memory will be lost. Schmidt therefore concludes, "If consciousness is indeed equivalent to the short term store, these amounts to a claim that storage without conscious awareness is impossible".The second stage is one in which intake is absorbed into the learner's interlanguage system and changes to this system only occur when language features become part of long-term memory.Chapter ⅢAttention and Second Language Vocabulary Acquisition ProcessV ocabulary entails less complicated and abstract grammatical rules compared with syntax. Therefore, it seems there is no need for too great amount of focal attention and external efforts, for learners can assimilate the new words by directly memorizing them. However, many other facts refute the above statement. More often than not, students complain the difficulty of memorizing a large number of words in a due period of time, and sometimes, even the learned words can not keep in the memory for an expecting long time ready for retrieval. A more demanding problem is that even if the learners know the meanings of the words, they can not put them into proper use. All of the above problems show that vocabulary acquisition is not just an easy case of memory. It requires much more external controlled attention to every aspects of a new word, ranging from pronunciation, spelling to collocation and usage in a real context. A large number of theoretical and empirical studies have been done to verify the effects of different methods and strategies to facilitate vocabulary learning. Laufer conclude that elaboration, the same concept as “processing depth”,is the most important factor affecting vocabulary acquisition. Their further argument is from William James’s (1890) notion that all improvement of the memory lies in the line of elaborating the associates. In other words, the more special attention learners pay to the form and semantic associates the deeper the words be processed and the more meaningful associates will be the previously existing knowledge in learners’ interlanguge system.ConclusionWe can say attention plays a very important role in vocabulary acquisition, for it is the prerequisite from input to intake and output. Besides, we can find that attention appears in the first place in the area of processing depth, for great elaboration for new words can help promote vocabulary acquisition from the perspective of quantity and quality of input, and then for deeper processing in working memory which in turn enhances good memory for convenient retrieval. Without focal attention to certain items, all of the input will just stay in working memory for a short period of time and then fall into oblivion.References:[1] Brown ,C. Factors affecting the acquisition of vocabulary: frequency and saliency of words[A]. 1993[2] Ellis, R. (1994). The Study of Second Language Acquisition. Oxford: Oxford University Press.[3] Kihlstrom, J. (1984). Conscious, subconscious, unconscious: A cognitive perspective. In K. Bowers & D. Meichenbaum (Eds.), The Unconscious Reconsidered . New York[4] Laufer, B.&K.Shmueli. Memorizing new words: Dose teaching have anything to do with it? RELC Journal.1997(1) /[5] Nation, I.S.P. Teaching and Learning Vocabulary [M]. New York; Newbury House. 2004[6] Robinson, P. (1995). Generalizability and automaticity of second language learning under implicit, incidental, enhanced, and instructed conditions.Studies in Second Language Acquisition (19). [7] Schmidt, R. (1990). The role of consciousness in second language learning. Applied Linguistics (11). /[8] Schmidt, R. (1994). Awareness and second language acquisition. Annual Review of Applied Linguistics (13) /[9] Tomlin,R&V.Villa. Attention in Cognitive Science and SLA[J]. Studies in Second Language Acquisition 1994 (16). [10] Williams,J.N.(1890).Learning without awareness./[11] 戴曼纯. 论第二语言词汇系的研究. 外语教学与研究.2000(2)[12] 刘世理. 论语言认识中的中的注意机制. 四川外国语大学学报. 2006.(4)[13] 王琦,杨文琴. 二语习得中的注意机制研究. 西北师范大学学报. 2009 (46)。
老师们赞不绝口的文献综述模板

老师们赞不绝口的文献综述模板一、引言问题陈述: 从宏观大背景出发,阐述研究此问题的必要性及重要性。
模板一: 作为时代的一股洪流,我们不得不认识到这一议题已然成为当前社会各界瞩目的热点话题,而随着社会不断演进和发展,它必将更加深刻地影响我们的社会进程。
本文着眼于理论与实践的交汇,旨在深入梳理与总结学界对这一议题的讨论与思考。
模板二: 卓越学者XXX,早在XXX年,就为我们献上了一部关于这一课题的丰富研究成果,并且持续耕耘数十载,为我们揭示出许多新的境界。
然而,尽管如此丰富的研究,却仍无法解决这一重要问题。
正如学者A在YYYY年指出的那样,学者B也在ZZZZ年明确指出,这一问题依然挥之不去。
这一未解之谜对学术研究产生了深远的影响,也在实际生活中具备着卓越的意义。
因此,本论文将在这一知识的白日之下,探究其学术价值和实践意义。
目的及意义模板: 近年来,我们已经看到了一个明显的趋势,这使得我们不得不意识到,在当前日益严峻的社会环境下,对这一议题的研究具有紧迫性和不可或缺的重要性。
这一议题已经成为了社会发展的重要组成部分,而如果我们不加以妥善处理,不仅将直接影响到我们社会的可持续发展,还可能引发各种潜在的矛盾和问题,对社会的健康进程造成直接的阻碍。
因此,本文试图以一种前瞻性的方式,深入探讨这一议题,基于详尽的研究,明晰其多方面原因,为我们提供有针对性的解决思路与方法,以期达到全面推动社会进步的目标。
对于文献的分类方法,建议不再局限于国内外文献的简单划分,而应根据主题和时间的划分,以更清晰地呈现文献的关联性和重要性。
1、主体划分分析论文专业层次,比如,建筑行业可以从工程质量、环境、参与人员、材料、资金等来描述;教育行业可以从教师政策、校园、家长等角度,对学术界相关观点梳理。
模板:关于乡村教育问题......谈到校园环境建设时指出.....在研究中运用了...调查梳理了...2、时间划分一般采用由远及近的方式,--般采用近5-10年的文献,并根据需要将其分阶段描述。
文献综述模板(模板)

北京化工大学北方学院毕业设计(论文)——文献综述(空一行) 文献综述 (空一行)前□□言 (空一行)本人毕业设计的论题为《电子商务在秦皇岛港务集团的规划分析》,由于目前国内外学者并没有对秦港集团的电子商务发展进行过规划分析,并且据了解秦港集团也没有实施电子商务系统,因此本文的叙述对秦港集团电子商务的规划具有一定的指导意义。
本文根据目前国内外学者对电子商务与物流运输及港口的研究成果,借鉴他们的成功经验,大胆的将电子商务规划到秦港集团的业务中。
这些文献给与本文很大的参考价值。
本文主要查阅进几年有关电子商务与物流运输的文献期刊。
(下页为具体内容:一般包括:国内与国外2部分内容)题目为“文献综述”上下各留一空行,宋体,三号字,居中,加粗。
行间距固定值22磅,段前、段后0行,无缩进。
前言之下留一空行,宋体,小三号字,居中,加粗。
行间距固定值22磅,段前、段后0行,无缩进。
“前言”二字中间空两格。
前言单独一页。
页脚插入页码,居中。
页码格式为“1,2,3,…”就到目前为止,国内学者的研究主要集中在以下几个方面:1、XXXXXXXXXX安旗和富森(2007)在《构建电子商务平台促进交通物流发展》中指出构件电子商务平台的必要性,这是符合现代信息技术革命正日益深刻地改变着社会生产和生活的现状。
并且是适应社会主义经济的需要。
李峻峰和苏小玲(2004)在《论电子商务对我国现代物流的影响及对策》中主要论述了……..更多学者的观点(下略)。
2、XXXXXXXXXX刘大军(2003)《浅谈物流运输管理与信息技术》中指出我国绝大多数运输企业在对信息技术的实际应用程度和应用效果方面都与欧美发达国家相差甚远。
我国物流运输企业在信息技术应用方面存在的问题严重地影响着企业业务管理能力和服务水平的进一步提高。
夏黎(2004)在《电子商务给物流业及其管理带来的变化》提出电子商务是一场商业领域的根本性革命,其自身的特点给中国企业带来的新的机遇。
文献综述范文

战略性贸易政策在我国金融服务贸易文献综述国际经济与贸易专业上个世纪90年代以来, 全球经济竞争的重点正从货物贸易转向服务贸易, 国际服务贸易日益显示着作为经济增长重要源泉的作用。
同时, 国际服务贸易结构也正走向高级化, 通信服务、保险服务、金融服务、计算机和信息服务等现代服务贸易己占到整个服务贸易的大部分。
而我国服务贸易优势部门主要集中在海运和旅游等比较传统的领域, 金融、保险、计算机服务等现代服务业的国际竞争力还很低。
同时, 中国的金融服务业也面临着如何逐步开放和如何有效保护的问题, 这就衍生出对金融服务贸易决策理论研究的需要。
因此, 借鉴国外学者先进的研究方法和研究成果, 紧密结合中国实际, 加强对中国金融服务贸易政策选择的研究, 具有重要的学术价值和很强的现实意义。
一、金融服务贸易相关文献综述(一)国外学者关于金融服务贸易的研究现状1、国际上自20世纪80年代初才开始正式对金融服务贸易进行研究, 但所取得的参考文献甚少, 迄今为止对哪种贸易理论适用于金融服务贸易也仍然存在很多不同观点。
其中主要有:2、外生比较优势模式世界银行国际贸易和资本流动司Sapir.A,and Lutz.E(1981)在其工作报告中提出了外生比较优势模式的实用性, 他们认为传统贸易理论作为一种简单思想, 完全适用于服务贸易, 亚当·斯密、李嘉图、赫克歇尔一俄林等的比较优势理论即可解释国际金融服务贸易的动因, 不必把服务贸易与货物贸易分开。
在实证方面, Sapir和Lutz(1981)收集了保险业的有关数据, 结果证明了他们的主张。
美国学者Walter.I(1988)在其论文《金融服务的全球竞争力: 市场结构、市场保护和贸易自由化》中通过银行业和证券业数据的分析研究也得出了相同的结论。
这种观点的早期代表人物还有B.Hidnl和A.Smith (1984)。
3、2. 内生比较优势模式4、这一观点认为比较优势可以通过后天专业化学习获得或通过投资创新与经验累积人为创造出来, 可由技术创新、资本积累、人力资本投资、合理的制度等决定。
文献综述的范文

文献综述的范文文献综述是对相关研究文献的查阅、收集、整理、综合、评价和分析的过程。
它能够帮助研究人员深入了解某一领域的研究现状和学术趋势,对于指导研究设计、研究方法的选择、结果的解释及推广应用具有十分重要的意义。
本文将介绍某个领域的相关研究成果以及未来研究的发展方向。
本领域的研究发现:这个领域主要研究的是人类和自然环境的相互作用,重要的领域还是全球环境变化,气候模拟和综合评价,文献综述表明,研究范围逐渐扩大,并涉及到更加细致的研究领域。
一些关键词包括气候变化、干旱、土地退化、能源管理、大气污染、生态系统管理、重金属污染、生态水文学、全球变化等等。
研究成果表明人类活动对环境的影响非常大,因此环境保护成为了一个国际性的问题。
未来研究方向:针对环境变化越来越紧迫的现状,未来的研究需要注重如何减少环境污染以及环境的演化过程。
一个主要的研究方向是整合人类和自然的影响,以更好地理解环境演变的进程。
另一个重要的方向是发展新的跨学科方法和模型,结合物理学、化学、生物学和社会学等学科,以提供更好的模拟、评估和规划工具,帮助实现环境可持续性。
此外,也需要开展更为深入的研究,探讨在这个过程中的一些特定问题,如生态地图、微观生态学等学问。
最终的目标是提高人类对环境演变过程的认识,为制定政策和法律提供更为科学的支持。
并应该不断改进和加强环保手段和措施的效果。
总结:环境问题是当今世界所面临的最大的问题之一。
对于解决环境问题的问题,需要一个对环境研究的综合方法,需要高效地整合资源,开展跨学科的研究工作,全力以赴解决这个难题。
为此,我们需要不断地完善现有的研究体系,加强合作与交流,找到合适的解决方案,以期到达解决环境问题的目标。
文献综述范文(通用5篇)

文献综述篇1一、引言叛逆心理是不健康的一种心理,如果家长、教师方面不能及时给予矫正,将会对他们的发展造成很不利的影响。
目前我国教育专家、学者们针对青少年青春期的叛逆心理一般都是从家长、老师们转变思想,耐心与青少年沟通以及加强社会文化现象方面着手的。
而社会文化现象方面到底怎么去引导,并没有提出实质性的方法,而社会引导这一方面在我看来,恰恰与家长和教师对青少年所做的引导起着一样重要的作用。
所以说,矫正青少年叛逆心理的这条道路,依然很漫长。
二、正文(一)叛逆心理的概念至今为止,关于叛逆心理这个定义还没有一个唯一的概念。
不过学者们普遍认同朱智贤在《心理学大辞典》中对叛逆心理的界定:客观环境与主题需要不相符合时所产生的一种心理活动,具有强烈的抵触情绪。
(二)叛逆心理的表现通常学者们认为青春期的孩子有2个主要方面在变化。
一个是从生理方面;另一个是在心理方面。
对于生理方面学者们一致都认为孩子在身体结构上在发育;心理上,青少年在得不到渴望的承认和理解时,常常表现为任性和耍小脾气,常常采用怀疑的眼光和敌视的态度来对待周围事物。
更严重者常常无视家长和老师的教育甚至用传播负能量来扰乱周围人的思维和态度,给自己和他人都造成不好的影响。
(三)叛逆心理的危害几乎所有青少年都会经历叛逆心理,它有什么危害呢?绝大部分学者对这一个关键性的问题却没有给予确切的说明。
处于叛逆期的青少年,他们的某些不恰当的行为和心理如果不加以纠正和引导,会导致其产生对抗社会、不合群等病态性格,甚至会进一步走向犯罪的道路。
也有无数案例也证明了严重逆反心理的危害。
如社会上多发的离家出走现象、自杀事件等都有力的说明了这一点,如果不在叛逆初期给予正确的引导,会引起多么严重的后果。
(四)青少年叛逆心理产生的原因对于青少年产生叛逆心理的原因众说纷纭,但是无一例外都提到了以下几种。
1、自身原因。
青少年在青春期的发育时期脑功能越来越发达,思维发展也也越来越迅速。
青少年由于到了一定的年龄,他们在生理上性意识以及性别意识都开始觉醒,性意识又进一步在心理上产生断乳,进而形成越来越强烈的独立意识。
文献综述范文3篇

文献综述范文
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文献综述的范文

⽂献综述的范⽂⽂献综述是在确定了选题后,在对选题所涉及的研究领域的⽂献进⾏⼴泛阅读和理解的基础上,对该研究领域的研究现状(包括主要学术观点、前⼈研究成果和研究⽔平、争论焦点、存在的问题及可能的原因等)、新⽔平、新动态、新技术和新发现、发展前景等内容进⾏综合分析、归纳整理和评论,并提出⾃⼰的见解和研究思路⽽写成的⼀种不同于毕业论⽂的⽂体。
⽂献综述的范⽂1 概述: 学前智育是由家长及幼师利⽤各种⽅法、实物为开发学前⼉童的智⼒,使他们更加聪明,有系统、有计划⽽且科学地对他们的⼤脑进⾏各种刺激,使⼤脑各部位的功能逐渐完善⽽进⾏的教育。
学前智育是学前教育学的重要内容之⼀,是构成学前教育学的科学体系的⼀部分。
⼉童是⼈⽣智⼒发展的基础阶段,⼜是发展最快的时期,适当、正确的学前教育对幼⼉智⼒及其⽇后的发展有很⼤的作⽤。
超常⼉童的形成、发展,⽆⼀不与适当、正确的学前教育有关,尤其是智⼒⽅⾯的学前教育。
学前智育是⼀个多⽅⾯的培养过程。
原则: 是对0岁⾄⼊⼩学前⼉童实施教育应遵循的基本要求。
幼⼉园教育⼯作的原则是:体、智、德、美诸⽅⾯的发展应互相渗透,有机结合;遵循幼⼉⾝⼼发展的规律,符合幼⼉的年龄特点,注重个体差异,因⼈施教,引导幼⼉个性健康发展;⾯向全体幼⼉,热爱幼⼉,坚持积极⿎励、启发诱导的正⾯教育;合理地综合组织各⽅⾯的教育内容,并渗透于幼⼉的⼀⽇⽣活各项活动中,充分发挥各种教育⼿段的交互作⽤;创设与教育相适应的良好环境,为幼⼉提供活动和表现能⼒的机会与条件以游戏为基本活动,寓教育于各项活动中。
依据0岁~6岁⼉童⾝⼼发展规律,学前教育的原则可概括为: (1)从胎教开始适应各年龄发展和个体发展的教育; (2)促进学前⼉童体、智、德、美的良好发展与个性的健康发展; (3)成⼈对学前⼉童的照管与教育相结合; (4)以兴趣诱发,在游戏中成长; (5)创设适宜的环境,发挥其教育的功能。
趋势: 简述 ⾃80年代以来,加强学前教育成为世界未来教育的主要⽬标之⼀。
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本科生毕业设计(论文)文献综述( 2007 届)题目:挠盘式圆葱移栽机的设计学生姓名黄晨帆学号 200702120920专业班级农业机械化及其自动化071学院名称工程学院指导教师刘建军年月日摘要圆葱在我国己成为区域规模种植的经济作物之一,由于圆葱移栽的农艺要求特殊性,国产的各种移栽机都不适合圆葱这类小株距作物的移栽,圆葱移栽机在国内的研究与应用方面还是空白。
为了实现圆葱葱机械化移栽,作者分析了国内各种移栽机的结构特点,确定了以挠性圆盘式栽植器为研究对象,在分析挠性圆盘式栽植器的运动轨迹和特征参数的基础上,完整地确立了挠性圆盘式移栽机的基本参数:栽植频率、栽植株距、机组前进速度、输送带上秧槽的间距、挠性圆盘半径、挠性圆盘的转速、夹苗株数以及传动比之间的相互关系,并建立了以葱苗栽植倾角Y=90。
为目标的优化设计数学模型,提出了挠性圆盘式大葱移栽机的优化设计方法。
优化结果表明,挠性圆盘式移栽机的栽植性能与两圆盘夹角、特征参数以及所栽植葱苗的直径和高度有关,并存在最佳组合。
在优化设计计算的基础上,作者设计了一台挠性圆盘式圆葱葱移栽机,田间试验结果不仅证明了挠性圆盘式移栽机可以实现圆葱的小株距移栽,完全能够满足圆葱栽植的农艺要求,而且检验了本文提出的挠性圆盘式圆葱移栽机的优化设计方法的可靠性.本文的研究结果对于挠性圆盘式移栽机的设计和使用具有重要的指导意义。
关键词:圆葱,移栽机,挠性圆盘,AbstractScalllion has become one of regional scale planting for many years inChina.unfottunately,because scallion is planted with a small spacing between seedings,all kinds of available transplanters made in domestic can not be used for transplanting scallion,so up to now planting has to be planted by manual tools.Based on the analysis of the kinetic track of the scallion during,basic relationships among the characreristic parameter,the rate of transplanting,the spacing between seedings,the angle of releading seedings,the diameter and length pf seedings,have been set up in this paper,and then a mathematic model of optimum design for the transplanter with the final planting angle of seedlings(γ=90°)has been formulated and solved with goog tesults.According to the optimum solutions,a new type of teansplanter with two flexible metal disks has been developed and the field tests of the transplanter have been conducted.The results not only indicate that the transplanter can plant scallion with small space,and meet the requirements of the scallion practical planting,but also demonstrate that the oprimum design method of the transplanter is correct and useful.The research results of this kind of transplanter in the paper are very important for the design and application in field practice.Key Word: scallion,transplanter,flexible metal disks前言大葱原产于亚洲西部高寒地区,在我国栽培历史悠久,遍布全国各地,是一种重要的蔬菜和调味品。
随着我国农业种植结构调整和大葱出口量逐年增加,许多地区都把大葱种植作为一项产业来发展,种植面积迅速扩大,成为区域规模种植的经济作物之一。
由于传统手工移栽作业的劳动强度高且生产率低,农民对大葱移栽的机械化要求越来越迫切,因此设计和研究大葱移栽机是非常必要的。
大葱栽植期一般在 5~7 月份,传统人工移栽分为插葱法和排葱法。
人工栽植的缺点是生产效率低,劳动强度高。
与其他移栽作物相比,大葱栽植的主要特点是:第一,小株距。
一般作物的栽植株距是 20~50cm,而大葱的株距仅有 5~10cm。
第二,深度较深。
一般作物的栽植深度为 3~5cm,而大葱的栽植深度为 6~10cm。
第三,不能窝根,由于葱白的质量决定了大葱的产品质量,因此要求栽植时不能窝根。
由于大葱移栽农艺要求的特殊性,现有的移栽机均难以实现大葱这类小株距作物的移栽。
为了实现大葱机械化移栽,在分析国内各种移栽机结构型式和特点的基础上,研制了一种挠盘式移栽机。
综述主题国外圆葱移栽机的现状由于圆葱主要在亚洲地区种植,因此相应的圆葱移栽机也很少,大部分集中在日本。
据调查,移栽机的机型有两种:一种是久保田公司生产的KN—P6半自动圆葱移栽机。
该机结构较小,由一人操作驾驶,并自走在垄沟内,用于圆葱的裸苗移栽。
该机主要由机架、开沟器、栽植器、镇压轮、输送带、苗箱及动力系统组成。
它采用双橡胶挠盘式移栽器,挠盘上部在导轮的作用下张开,下部在压紧滚轮的作用下闭合。
工作时,由人工背向喂苗,通过横向输送带将秧苗送至张开的橡胶挠盘中间,在挠盘的转动下使秧苗旋转90°移栽入土,同时覆土镇压轮从两侧覆土并进行镇压。
栽植深度一般在3~10cm可调,适合栽植15~40cm 高的裸苗,生产效率在0.013~0.02hm2/h之间。
该机结构简单、作业方便,但生产效率较低,而且橡胶挠盘使用寿命较短。
另一种是由みのる公司生产的OP290/2100全自动圆葱移栽机。
该机由一人手扶驾驶走在已整好的垄台上,一次作业完成两行或四行移栽,主要用于大葱的盘育钵苗栽植作业。
该机是采用双金属挠盘式移栽器,从喂苗到开沟、栽植、覆土和压密完全是自动化。
工作中采用特殊穴盘育出的钵苗,钵苗高度在8~20cm。
其工作过程是:装苗架上的钵苗秧盘自动进给,由专门的推苗机构向外推出一排钵苗,并通过曲柄连杆机构实现钵苗顺时针旋转180°,使钵苗放置到带分格的横向输送带上,完成喂苗作业。
在横向输送带末端有一个输出爪,定时运动实现分苗,将钵苗送至两个相对旋转的纵向输送带之间,并向下运输到两个相对回转的挠性圆盘栽植器中。
随着挠性圆盘的转动将钵苗逆时针旋转90°,同时钵体进入开沟器已开好的垄沟里,并由倾斜的覆土镇压轮进行扶正压实,完成整个栽植过程。
该机的特点是实现了栽植过程的全部自动化,生产效率高,而且株距准确、可调。
栽植深度在1~4cm范围内可以调节,株距在5~9cm范围内调节,生产效率为0.1hm2/小时。
但是,以上两种机型未在我国推广的原因主要有两方面:一是由于日本的葱苗培育方式与我国的不同,多为钵苗。
日本大葱大都采用温室穴盘育苗,从种子丸粒化、穴盘加装基质到穴内播种等环节都有配套机械。
用基质加装机充填穴盘基质,用穴盘精密播种机进行穴盘穴孔播种,在葱苗生长的全过程内实现对温度、湿度、光照、喷水和施肥等的自动控制,形成完整的工厂化育苗体系。
由此既保证了葱苗的质量,又可适时培育出大量健壮的葱苗。
而我国现有的育苗作业均由人工完成,无法与其配套。
二是进口机器价格很高,通用性差,很难适应中国农民的实际经济承受能力。
国内圆葱移栽机的现状国内从上世纪六十年代开始研制移栽机。
北京、辽宁、吉林、黑龙江、陕西、山西、江苏、河南、内蒙等全国二十多个省、市、自治区都先后研制出栽植玉米、棉花、甜菜、蔬菜等作物的移栽机,但是所设计使用挠性圆盘式移栽机的并不多。
1975年由邢台地区农机研究所、宁晋县农具研究所、华北农机学院联合研制了机械分秧式小麦移栽机[5l(双橡胶盘式),应用于小麦的裸根移栽,但没有推广。
1978年乌盟农机研究所研制了ZzT一2型甜菜移栽机Ie](双橡胶盘式);1978年北京农机所研制了ZzG一2型玉米、高粱移栽机[v](橡胶一金属盘式);在九十年代新疆农科院农机化所和黑龙江省红兴隆农垦管理局仿照日本的CT-4S型甜菜移栽机分别研制了两种2ZT一2型纸筒甜菜移栽机 (双橡胶盘式)。
以上所设计的移栽机多为双橡胶盘或橡胶一金属盘式,工作时依靠扇形板控制夹苗位置和夹苗时间,因此可控制释放的时间和位置。
早期机型由于人工送秧,效率较低,还会产生较大的株距变异,熟练的栽植手每人只能送秧450株/min。
但是,到目前为止,国内在挠性圆盘式移栽机方面存在的主要问题是:(l)以往的研制工作都不是以圆葱为栽植对象来进行的,采用挠性圆盘式移栽机能否实现大葱的小株距机械化移栽,仍然是面临的一大挑战。
(2)过去的研制工作基本上还停留在试制和试验阶段,关于挠性圆盘式移栽机的工作原理、设计方法和秧苗的运动规律方面的深入研究尚未见到报道。
总结综上所述,我国在针对圆葱这样的小株距移栽机的研制开发上还是空白。
要研制高效的圆葱移栽机还必须与育苗技术结合起来,不能独立进行。
我国研制的各种移栽机没有推广应用的主要原因之一,就是栽植机械与育苗技术脱节、移栽机与秧苗不配套。
如果这个问题不解决,国产移栽机就难以推广。
因此,研制开发自动化程度高、通用性好的大葱移栽机就必须首先解决育苗技术,才能更好地设计生产高效的移栽机。
同时还应看到,从现阶段我国国情考虑,研制半自动化的移栽机在农村将有广阔的市场。
半自动移栽机尽管栽植速度不快,还需要一定的人力,但是它结构简单、价格低、适应性好、使用方便,适应我国国情,所以,圆葱移栽机暂时还是应研制半自动式的,以适应农村机械化的发展。