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   64970篇
  免费   2637篇
  国内免费   20篇
  2020年   620篇
  2019年   809篇
  2018年   1080篇
  2017年   1102篇
  2016年   1184篇
  2015年   870篇
  2014年   1059篇
  2013年   5009篇
  2012年   1871篇
  2011年   2056篇
  2010年   1281篇
  2009年   1314篇
  2008年   1823篇
  2007年   1863篇
  2006年   1674篇
  2005年   1484篇
  2004年   1404篇
  2003年   1324篇
  2002年   1448篇
  2001年   2039篇
  2000年   2006篇
  1999年   1545篇
  1998年   774篇
  1997年   711篇
  1996年   686篇
  1993年   649篇
  1992年   1327篇
  1991年   1206篇
  1990年   1189篇
  1989年   1101篇
  1988年   1086篇
  1987年   1047篇
  1986年   1113篇
  1985年   1112篇
  1984年   960篇
  1983年   876篇
  1982年   662篇
  1981年   651篇
  1979年   1021篇
  1978年   768篇
  1975年   870篇
  1974年   902篇
  1973年   969篇
  1972年   828篇
  1971年   785篇
  1970年   691篇
  1969年   708篇
  1968年   897篇
  1967年   822篇
  1966年   698篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
73.
74.
75.
76.
77.
78.
79.
Public goods theories highlight an incentive system that rewards ‘free riding’ on the contributions of early contributors toward collective actions. However, because such theories focus on creation of the good, they may underestimate returns that accrue to early contributors subsequent to the good's realization. The concept of formative investment is introduced here to describe the extent to which organizations help to create public goods such as interorganizational linkages like participatory federations. Data from the CEOs of 48 organizations involved in a participatory federation were used to assess how an organization's level of formative investment is related to later patterns of dependency and interaction among federation members. Findings suggest that from a long‐term perspective, and for goods that involve communication and interaction, the incentive structure may not be so favorable for free riders. To the extent that organizations with high formative investment have the capability to envision the future and communicate that vision to potential federation partners, they may be able to both reduce free riding and secure for themselves advantageous positions in the subsequent network of relations.  相似文献   
80.
In Experiment 1, rats were trained on a discrimination between rubber- and sandpaper-covered arms of a maze after one group had been pre-exposed to these intra-maze cues. Pre-exposure facilitated subsequent discrimination learning, unless the discrimination was made easier by adding further discriminative stimuli, when it now significantly retarded learning. In Experiment 2, rats were trained on an extra-maze spatial discrimination, again after one group, but not another, had been pre-exposed to the extra-maze landmarks. Here too, pre-exposure facilitated subsequent discrimination learning, unless the discrimination was made substantially easier by arranging that the two arms between which rats had to choose were always separated by 135°. The results of both experiments can be explained by supposing that perceptual learning depends on the presence of features common to S+ and S-.  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