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   25673篇
  免费   205篇
  国内免费   21篇
教育   18658篇
科学研究   2804篇
各国文化   131篇
体育   1528篇
综合类   6篇
文化理论   481篇
信息传播   2291篇
  2021年   143篇
  2020年   202篇
  2019年   290篇
  2018年   2533篇
  2017年   2469篇
  2016年   1968篇
  2015年   394篇
  2014年   440篇
  2013年   2498篇
  2012年   542篇
  2011年   1091篇
  2010年   1158篇
  2009年   673篇
  2008年   930篇
  2007年   1417篇
  2006年   312篇
  2005年   604篇
  2004年   693篇
  2003年   585篇
  2002年   314篇
  2001年   459篇
  2000年   330篇
  1999年   264篇
  1998年   124篇
  1997年   176篇
  1996年   144篇
  1995年   129篇
  1994年   153篇
  1993年   120篇
  1992年   189篇
  1991年   206篇
  1990年   197篇
  1989年   204篇
  1988年   171篇
  1987年   160篇
  1986年   170篇
  1985年   212篇
  1984年   162篇
  1983年   149篇
  1982年   129篇
  1981年   125篇
  1980年   116篇
  1979年   163篇
  1978年   135篇
  1977年   118篇
  1976年   96篇
  1975年   113篇
  1974年   100篇
  1973年   107篇
  1971年   99篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
981.
982.
The slow neutron-induced radioactivities of nuclear explosions have been evaluated for infinite media of filtered Schuylkill water and the earth's crust. The magnitudes of these effects are compared with the activity of the fission fragments, and the conditions under which they may be of importance are considered.It has been assumed that a gram-molecule of neutrons is liberated in the blast.  相似文献   
983.
984.
It is often desirable to represent carrier distribution systems by networks so that analysis can be made to predict the behavior of these systems. Modeling of two canonical carrier distribution systems, the star-shaped system and the parallel-wire system by networks was carried out in this paper. The representation is given in terms of lumped parameters when the lengths of the carrier lines are short and it is given in terms of lumped and distributed parameters when the lengths of the carrier lines are long.  相似文献   
985.
The influence of negative, equal, and positive social comparison and of nonsocial comparison upon 4- and 5-year-old black children's subsequent aggressive and regressive behavior in 3-member groups was investigated. The group behavior of boys included more physical agression following negative social comparison than the other treatments, and their group behavior also consisted of more nonverbal teasing behavior following the negative comparison treatment than that of the equal and nonsocial comparison groups. When the behavior of the nontarget partners was controlled, children initiated more physical aggression, nonverbal teasing, and regression after experiencing negative social comparison with the partners than after following the other treatments. There was some evidence to support the reciprocal influence of children's aggressive behavior on each other, particularly for boys following imbalanced social comparison treatments.  相似文献   
986.
48 healthy neonates born to multiparae were randomly assigned to view a moving stimulus either in the horizontal or the upright position, with or without added vestibular stimulation and with or without pacifier sucking. The infant was shown a moving black line inside a strictly controlled visual environment provided by an apparatus which permitted horizontal and upright positioning and displacement of the infant. Visual tracking was recorded by a concealed TV camera positioned at a constant distance and angle from the infants' eyes in both positions. Quality of tracking during each of 4 trials was scored on a 7-point scale. Results indicate that vestibularproprioceptive stimulation provided to the infant either horizontally or semivertically significantly enhanced his visual tracking, whereas the upright position did not. Pacifier sucking also improved his performace.  相似文献   
987.
988.
989.
990.
In this paper, the stability equation method is applied to the analysis of nonlinear systems with characteristics equations having complex coefficients. Three types of systems are studied: those with unstable open-loop poles, unstable characteristics roots or an equal number of open-loop poles and zeros.  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