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   62977篇
  免费   2617篇
  国内免费   21篇
  2020年   626篇
  2019年   838篇
  2018年   1144篇
  2017年   1180篇
  2016年   1243篇
  2015年   901篇
  2014年   1045篇
  2013年   4738篇
  2012年   1963篇
  2011年   2128篇
  2010年   1296篇
  2009年   1292篇
  2008年   1888篇
  2007年   1889篇
  2006年   1704篇
  2005年   1510篇
  2004年   1406篇
  2003年   1325篇
  2002年   1424篇
  2001年   2006篇
  2000年   2002篇
  1999年   1524篇
  1998年   736篇
  1997年   649篇
  1996年   641篇
  1993年   574篇
  1992年   1257篇
  1991年   1154篇
  1990年   1138篇
  1989年   1045篇
  1988年   1023篇
  1987年   980篇
  1986年   1051篇
  1985年   1071篇
  1984年   890篇
  1983年   806篇
  1982年   570篇
  1981年   572篇
  1979年   948篇
  1978年   677篇
  1975年   770篇
  1974年   822篇
  1973年   919篇
  1972年   773篇
  1971年   731篇
  1970年   650篇
  1969年   678篇
  1968年   866篇
  1967年   782篇
  1966年   660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