首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   59256篇
  免费   2375篇
  国内免费   31篇
  61662篇
  2020年   668篇
  2019年   854篇
  2018年   1196篇
  2017年   1213篇
  2016年   1297篇
  2015年   873篇
  2014年   1083篇
  2013年   5320篇
  2012年   1917篇
  2011年   2051篇
  2010年   1230篇
  2009年   1248篇
  2008年   1875篇
  2007年   1850篇
  2006年   1649篇
  2005年   1506篇
  2004年   1492篇
  2003年   1352篇
  2002年   1429篇
  2001年   1840篇
  2000年   1742篇
  1999年   1379篇
  1998年   779篇
  1997年   676篇
  1996年   617篇
  1995年   627篇
  1994年   586篇
  1993年   602篇
  1992年   1102篇
  1991年   1038篇
  1990年   1016篇
  1989年   921篇
  1988年   861篇
  1987年   854篇
  1986年   869篇
  1985年   931篇
  1984年   762篇
  1983年   679篇
  1982年   566篇
  1981年   554篇
  1980年   525篇
  1979年   770篇
  1978年   603篇
  1976年   536篇
  1975年   679篇
  1974年   722篇
  1973年   658篇
  1972年   601篇
  1968年   584篇
  1967年   577篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
In this paper a method is outlined for measuring the diversity of the results of applied R&D with the use of IPC (International Patent Classification). The method has been tested in the contexts of the academic physical, engineering, and chemical institutes. The trend of applied research at a given institute increases both at the level of classes and subclasses, and at the IPC level. Inventions developed within specializations at each institute have a greater efficiency than other forms of inventive activity. The objective was to seek the optimal extent of diversification of applied R&D, which would simultaneously ensure the preservation of the scientific specialization of an institute, the high level of scientific research associated with developing innovations, and the high overall efficiency of each institute.  相似文献   
992.
This paper is concerned with the processing of informal arguments, that is, arguments involving probable truth. A model of informal argument processing is presented that is based upon Hample's (1977) expansion of Toulmin's (1958) model of argument structure. The model postulates that a claim activates an attitude, the two components forming a complex that in turn activates reasons. Furthermore, the model holds occurrence of the reason, or possibly the claim and the reason, activates values. Three experiments are described that provide support for the model.This research was supported by the Mellon Foundation and by the Office of Educational Research and Improvement of the Department of Education via an award for the Center for the Study of Learning to the Learning Research and Development Center. The contents of the paper are not necessarily the position of any of these organizations.  相似文献   
993.
Being unreasonable: Perelman and the problem of fallacies   总被引:1,自引:0,他引:1  
Most work on fallacies continues to conceptualize fallacious reasoning as involving a breach of a formal or quasi-formal rule. Chaim Perelman's theory of argumentation provides a way to conceptualize fallacies in a completely different way. His approach depends on an understanding of standards of rationality as essentially connected with conceptions of universality. Such an approach allows one to get beyond some of the basic problems of fallacy theory, and turns informal logic toward substantive philosophical questions. I show this by reinterpreting three so-called fallacies - theargumentum ad baculum, equivocation and composition/division - in the light of Perelman's account.  相似文献   
994.
In the mid 1980s it was apparent that the need for organ donors exceeded those willing to donate. Some University of Pittsburgh Medical Center (UPMC) physicians initiated discussion of possible new organ donor categories including individuals pronounced dead by traditional cardiac criteria. However, they reached no conclusion and dropped the discussion. In the late 1980s and the early 1990s, four cases arose in which dying patients or their families requested organ donation following the elective removal of mechanical ventilation. Controversy surrounding these cases precipitated open discussion of the use of organ donors pronounced dead on the basis of cardiac criteria. Prolonged deliberations by many committees in the absence of precedent ultimately resulted in what is, to our knowledge, the country's first policy for organ donation following elective removal of life support. The policy is intricate and conservative. Care was taken to include as many interested parties as possible in an effort to achieve representative and broad based support. This paper describes the development of the UPMC policy on non-heart-beating organ donation.  相似文献   
995.
996.
This article describes an important new area of research on services for children and adolescents with mental disorders at the National Institute of Mental Health, the parameters of mental health services research for youth, and the opportunities that are available for grant-funded investigations in this area.  相似文献   
997.
To determine the frequency and correlates of nonsuicidal physically self-damaging acts in 12–14 year olds, a two stage epidemiologic survey with a self-administered questionnaire (N=3283) followed by a psychiatric interview of a subsample of the adolescents and their parents (N=444) was used. Prevalence estimates of interview validated nonsuicidal physically self-damaging acts were 2.46% in males and 2.79% in females. Significant relationships were found between nonsuicidal physically self-damaging acts and suicidal ideation, major depression and undesirable life events. Data suggest that physically self-damaging acts occur at substantial rates during early adolescence. The strong correlation between nonsuicidal self-destructive acts and both suicidal ideation and major depression clarifies prior conflicting reports in the literature and suggests that a history of self-damaging acts should be taken into consideration when evaluating for possible depression and suicide risk.  相似文献   
998.
Direct-observation procedures were used to objectively and efficiently assess several classes of service provided for individuals residing at two state facilities for the developmentally disabled. Time samples were taken of the condition of the clients' physical environment and of the clients themselves. The ongoing behavior of both clients and staff also was recorded. Each residence was observed at least three times during both regular work hours and evening/weekend hours. Results showed that both facilities scored high in the categories regarding the physical condition of the living areas, as well as the categories concerning the condition of the clients. Greater variability was seen in the data on client and staff behavior. More generally, the results indicate that time-sampling procedures can be used efficiently to collect data on multiple aspects of service delivery for large numbers of individuals.  相似文献   
999.
1000.
Commercial database programs such as dBase and Paradox, although developed originally for business applications, are versatile and powerful tools that can be used for an academic purpose such as evaluating student performance. They can be used to write and store test questions, assemble and print classroom or on-line laboratory tests, and calculate grades, test statistics, and so forth. Databases are flexible, unlike textbook “ancillary” test bank programs that are inextricably bound to the strictly linear format and brief shelf life of specific textbook editions. A prototypical relational database program is described, with which an instructor can produce tests based on generic terms adapted from Boneau’s (1990) study of psychological literacy, as well as on behavioral learning objectives adapted from Bloom’s (1956) taxonomy of educational objectives. As a relational database, the program integrates terms, objectives, questions, tests, and test scores, and avoids unnecessary data duplication and waste of computer storage space.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号