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   20252篇
  免费   216篇
  国内免费   26篇
教育   14068篇
科学研究   2439篇
各国文化   153篇
体育   1380篇
综合类   33篇
文化理论   318篇
信息传播   2103篇
  2022年   119篇
  2021年   189篇
  2020年   274篇
  2019年   393篇
  2018年   1199篇
  2017年   1221篇
  2016年   972篇
  2015年   399篇
  2014年   508篇
  2013年   2788篇
  2012年   563篇
  2011年   693篇
  2010年   646篇
  2009年   477篇
  2008年   534篇
  2007年   654篇
  2006年   330篇
  2005年   388篇
  2004年   428篇
  2003年   344篇
  2002年   293篇
  2001年   381篇
  2000年   404篇
  1999年   300篇
  1998年   189篇
  1997年   220篇
  1996年   219篇
  1995年   141篇
  1994年   158篇
  1993年   134篇
  1992年   236篇
  1991年   224篇
  1990年   238篇
  1989年   240篇
  1988年   217篇
  1987年   216篇
  1986年   200篇
  1985年   240篇
  1984年   185篇
  1983年   153篇
  1982年   154篇
  1981年   127篇
  1980年   127篇
  1979年   204篇
  1978年   158篇
  1977年   135篇
  1975年   106篇
  1974年   115篇
  1973年   104篇
  1971年   106篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
This paper surveys the trends in industrial R&D in India over the last two decades. It shows that there has been a rapid rise in R&D expenditure and a shift in its composition towards in-house corporate R&D and away from R&D in government laboratories, which is explained by the laboratories' lack of market orientation and manufacturing experience. According to cross-section studies of corporate R&D, larger companies aim towards larger technological advances and take a longer view; but the overall composition of corporate R&D shows no discernible change. This apparent inconsistency is explained by the development of the technology market. Much R&D was triggered off by the need for import replacement arising from import controls till 1965 and later by the need for product diversification in the recession. But construction of new plants and mechanization for speeding up operations, activities where sustained R&D can yield large firms a steady flow of innovations, were unimportant or infrequent, and the demand for technology they gave rise to was largely met by imports.  相似文献   
72.
Necessary and sufficient conditions are obtained for the realization of an m-variable positive real function (PRF) as the impedence function of a resistively-terminated ladder network of m lossless two-ports connected in cascade. Each two-port is a single-variable lossless ladder with all of its transmission zeros either at the origin or at finity. Conditions are also obtained when each of the two-ports is a Fujisawa-type lowpass ladder.  相似文献   
73.
74.
75.
76.
In an attempt to clarify the chronological relationship between identity and equivalence conservation, normal preschool-aged children (experiment 1) were exposed to brief videotape demonstrations of a model conserving identity and equivalence, identity only, equivalence only, or neither. Subsequent performances indicate that identity was easier to accelerate than equivalence, and training in both identity and equivalence appeared to be most effective in accelerating conservation. Trainable mentally retarded (TMR) children were then exposed to either the identity-equivalence-conserving or control model (experiment 2). This population, which some have argued remains at a preoperational level of functioning, was more likely to conserve identity than equivalence. In addition, conservation in the training group increased following training, though these gains were not maintained over a 3-week retention interval.  相似文献   
77.
First-grade males performed a 30-min visual vigilance task under 5 conditions of auditory background stimulation. The 5 conditions consisted of (1) continuous conversation, in which subjects listened to a tape of conversation spliced so that there were no intervals of silence lasting longer than 3 sec; (2) continuous reverse, in which subjects heard the continuous conversation tape played in reverse; (3) intermittent conversation, in which subjects heard alternating segments of conversation and silence; (4) intermittent reverse, in which subjects heard alternating segments of reverse conversation and silence; and (5) silence control. Compared with silence or continuous stimulation, intermittent stimulation produced better detection regardless of whether or not it was meaningful. High achievers made more correct detections than low achievers, but only in the second and third time periods. Few subjects made errors of commission.  相似文献   
78.
79.
80.
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