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   4679篇
  免费   105篇
  国内免费   14篇
  4798篇
  2012年   538篇
  2011年   565篇
  2010年   138篇
  2009年   61篇
  2008年   450篇
  2007年   417篇
  2006年   406篇
  2005年   287篇
  2004年   269篇
  2003年   271篇
  2002年   229篇
  2001年   146篇
  2000年   188篇
  1999年   84篇
  1998年   22篇
  1997年   12篇
  1996年   11篇
  1995年   11篇
  1994年   15篇
  1993年   12篇
  1992年   15篇
  1990年   9篇
  1989年   9篇
  1988年   19篇
  1987年   9篇
  1986年   10篇
  1985年   17篇
  1984年   17篇
  1983年   10篇
  1982年   20篇
  1981年   16篇
  1980年   6篇
  1979年   11篇
  1978年   11篇
  1977年   7篇
  1976年   7篇
  1975年   8篇
  1972年   6篇
  1965年   8篇
  1958年   41篇
  1957年   39篇
  1956年   59篇
  1955年   36篇
  1954年   43篇
  1953年   42篇
  1952年   42篇
  1951年   37篇
  1950年   22篇
  1949年   19篇
  1948年   13篇
排序方式: 共有4798条查询结果,搜索用时 15 毫秒
461.
资本主义下的异化问题   总被引:5,自引:0,他引:5  
资本主义对个性产生影响的中心问题是异化现象。异化是一种体验方式,在这种体验中个人觉得自己是一个外人,或如人们说的他变得和自己疏远起来。他体验不到自己是自我世界的中心、自己行动的创造者——而他的行动和行动的结果却变成了  相似文献   
462.
In Experiment 1 six monkeys were tested with discriminative relations that were backward relative to their training in a 0-second conditional (“symbolic”) matching procedure. Although there was some indication of backward associations, the evidence was generally weak, and statistical evaluations did not reach conventional significance levels. Unlike children, who show backward associations to the point of symmetry, monkeys and pigeons display at best only weak and transient backward associations. In Experiment 2 associative transitivity was assessed across two sets of conditional matching tasks. All four monkeys tested demonstrated strong transitivity. In contrast, in Experiment 3 there was no evidence of transitivity in three pigeons tested under conditions closely comparable to those of Experiment 2. These results may identify some key features of interspecies differences and contribute to analyses of serial learning in animals.  相似文献   
463.
Pigeons' responses were reinforced on two identical and concurrently available chain variable-interval-schedules. Unlike the typical concurrent chains procedure, both links were operative throughout, thus producing three types of concurrency: (1) concurrent initial links; (2) concurrent initial and terminal links; (3) concurrent terminal links. Choice proportions in each of these three states suggested that the pigeons were sensitive to momentary likelihoods of reinforcement: choice proportions for a schedule were higher when the schedule had been operative for some time, resulting in a higher probability of reinforcement. The study also showed that the relative rates of responding did not match the relative rates of reinforcement in any of the three states of concurrency. Instead, the choice proportions in both the concurrent initial and in the concurrent terminal links were intermediate between the scheduled and the obtained relative rates of reinforcement, while the choice proportions for a terminal link concurrent with an initial link consistently overmatched the relative interreinforcement times (and were typically 1.00). These data indicate that an accurate characterization of choice may not be obtained by considering only the relative interreinforcement interval where one interreinforcement interval is segmented into a chain. Instead, the organism's choice for a schedule will be substantially lowered by the chaining operation.  相似文献   
464.
465.
Pigeons' responses in the presence of two concurrently available (initial-link) stimuli produced one of two different (terminal-link) stimuli according to identical but independent variable-interval schedules. Responding in the mutually exclusive terminal links was reinforced with food according to fixed-ratio schedules for six pigeons and according to fixed-interval schedules for two pigeons. None of the pigeons matched the proportion of (choice) responses in the initial links to the proportion of the rates of reinforcement obtained during the terminal links. Instead, as the values of each of the terminal-link schedules were increased by a constant amount, the choice proportions for the stimulus associated with the smaller of the two values increased, even though the relative rates of reinforcement during the terminal links decreased. These results are incompatible with those from previous studies with aperiodic (variable-interval or variable-ratio) schedules. The present results do suggest, however, that in transforming aperiodic schedules into their periodic equivalents, it may be necessary to consider the size of the smallest interreinforcement interval comprising the terminal-link schedules.  相似文献   
466.
467.
Humanity entered the twenty-first century with revolutionary achievements in biomedical research. At the same time multiple “dual-use” results have been published. The battle against infectious diseases is meeting new challenges, with newly emerging and re-emerging infections. Both natural disaster epidemics, such as SARS, avian influenza, haemorrhagic fevers, XDR and MDR tuberculosis and many others, and the possibility of intentional mis-use, such as letters containing anthrax spores in USA, 2001, have raised awareness of the real threats. Many great men, including Goethe, Spinoza, J.B. Shaw, Fr. Engels, J.F. Kennedy and others, have recognized that liberty is also a responsibility. That is why the liberty to decide now represents an acknowledged necessity: biomedical research should be supported, conducted and published with appropriate measures to prevent potential “dual use”. Biomedical scientists should work according to the ethical principles of their Code of Conduct, an analogue of Hippocrates Oath of doctors; and they should inform government, society and their juniors about the problem. National science consulting boards of experts should be created to prepare guidelines and control the problem at state level. An international board should develop minimum standards to be applicable by each country. Bio-preparedness is considered another key-measure.  相似文献   
468.
Israel has a long history of concern with chemical and biological threats, since several hostile states in the Middle East are likely to possess such weapons. The Twin-Tower terrorist attacks and Anthrax envelope scares of 2001 were a watershed for public perceptions of the threat of unconventional terror in general and of biological terror in particular. New advances in biotechnology will only increase the ability of terrorists to exploit the burgeoning availability of related information to develop ever-more destructive bioweapons. Many areas of modern biological research are unavoidably dual-use by nature. They thus have a great potential for both help and harm; and facilitating the former while preventing the latter remains a serious challenge to researchers and governments alike. This article addresses how Israel might best (1) prevent hostile elements from obtaining, from Israel’s biological research system, materials, information and technologies that might facilitate their carrying out a biological attack, while (2) continuing to promote academic openness, excellence and other hallmarks of that system. This important and sensitive issue was assessed by a special national committee, and their recommendations are presented and discussed. One particularly innovative element is the restructuring and use of Israel’s extensive biosafety system to also address biosecurity goals, with minimal disruption or delay.  相似文献   
469.
Motivational characteristics are influential in shaping adolescents' desire to persist in sport or to discontinue their sport participation. Self-determination theory (Deci & Ryan, 2000) was utilized as the theoretical framework for this study. This theory examines whether sustained participatory involvement, defined as continued participation in the sport through the next year, was influenced by individuals' self-determined motivation and by the fulfillment of the three basic psychological needs of autonomy, competence, and relatedness. Four hundred ninety two soccer players between the ages of 13 and 17 years comprised the sample. Results indicated sport dropout was explained by higher levels of amotivation, external regulation, and introjected regulation and by lower satisfaction of relatedness and autonomy needs. The findings of this study contribute to the knowledge base on sport dropout as they supported many of self-determination theory.  相似文献   
470.
The goal of this research is to describe the visual search patterns for diverse traffic signs. Twelve drivers of both genders and different driving experience levels took part in real driving research with an instrumented car provided with an eye-tracking system. Looking at signs has a weak relation with speed reduction in cases where actual driving speed was higher. Nevertheless, among the people who looked at the sign, the percentage of those who reduce the speed below the limit is greater than of those who do not look at the sign. Guide traffic signs, particularly those mounted over the road, are more frequently glanced at than speed limit signs, with a glance duration of more than one second, in sequences of more than two consecutive fixations. Implications for driving and the possibilities and limitations of eye movement analysis for traffic sign research are discussed.  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