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   5796篇
  免费   178篇
  国内免费   172篇
系统科学   302篇
丛书文集   113篇
教育与普及   47篇
理论与方法论   29篇
现状及发展   1018篇
研究方法   33篇
综合类   4593篇
自然研究   11篇
  2023年   53篇
  2022年   76篇
  2021年   73篇
  2020年   63篇
  2019年   36篇
  2018年   33篇
  2017年   50篇
  2016年   75篇
  2015年   147篇
  2014年   153篇
  2013年   156篇
  2012年   285篇
  2011年   309篇
  2010年   139篇
  2009年   150篇
  2008年   144篇
  2007年   164篇
  2006年   152篇
  2005年   300篇
  2004年   590篇
  2003年   570篇
  2002年   282篇
  2001年   175篇
  2000年   215篇
  1999年   178篇
  1998年   83篇
  1997年   75篇
  1996年   53篇
  1995年   55篇
  1994年   38篇
  1993年   32篇
  1992年   67篇
  1991年   48篇
  1990年   57篇
  1989年   51篇
  1988年   53篇
  1985年   37篇
  1979年   61篇
  1978年   39篇
  1975年   38篇
  1974年   56篇
  1973年   49篇
  1972年   50篇
  1971年   66篇
  1970年   54篇
  1969年   68篇
  1968年   59篇
  1967年   41篇
  1966年   55篇
  1965年   41篇
排序方式: 共有6146条查询结果,搜索用时 616 毫秒
441.
An improved double-threshold method based on gradient histogram   总被引:2,自引:0,他引:2  
This paper analyzes the characteristics of the output gradient histogram and shortages of several traditional automatic threshold methods in order to segment the gradient image better. Then an improved double-threshold method is proposed, which is combined with the method of maximum classes variance, estimatingarea method and double-threshold method. This method can automatically select two different thresholds to segment gradient images. The computer simulation is performed on the traditional methods and this algorithm and proves that this method can get satisfying result.  相似文献   
442.
This paper introduces the cost sensitive feature weighting strategy and its application in intrusion detection. Cost factors and cost matrix are proposed to demonstrate the misclassification cost for IDS. How to get the whole minimal risk. is mainly discussed in this paper in detail. From experiments, it shows that although decision cost based weight learning exists somewhat attack miselassifieation, it can achieve relatively low misclassification costs on the basis of keeping relatively high rate of recognition precision.  相似文献   
443.
444.
445.
446.
The localization of several muscle proteins in relaxed and contracted myofibrils is compared. The morphology of the myofibrils and the behavior of these proteins was also investigated under extraction conditions.  相似文献   
447.
448.
449.
The U-Pb isotope compositions of rutile, omphacite and garnet in the eclogite from the Jinheqiao area in the Southern Dabie ultrahigh-pressure metamorphic zone were analyzed. The consistent high precision U-Pb age (218 ± 1.2) Ma of rutile in eclogite from the Dabie Mountains was obtained by two ways of isochron and common Pb correction based on the composition of omphacite. This proves that the omphacite in eclogite has a U/Pb ratio (m = 2.8) low enough to be used for common Pb correction in the analyses of rutile. Under the rapid cooling condition (40℃/Ma) the closure temperature for U-Pb diffusion in rutile is about 470℃. Thus, this U-Pb age of rutile proves that 218 Ma should be the cooling age of eclogite at 470℃ instead of the peak metamorphic age.  相似文献   
450.
Calcineurin (CN) is thought to play a role in the synaptic plastivity and long-term potentiation (LTP) in the hippocampus. Based on two LTP models in vivo, a specific inhibitor cyclosporin A (CsA) of CN was observed, which affected LTP in the hippocampal dentate gyrus of the rats. The results indicated that CsA blocked LTP induced by high frequency stimulation (HFS) partly, but it had no effect on the decrease of the onset and peak latency of population spikes (PS) except that it reduced the increase of the amplitude after HFS. On the other hand, CsA blocked LTP induced by ginsenosides (GSS) completely. It suppressed the GSS-enhanced amplitude of PS reversibly and blocked the decrease of the peak latency of PS induced by the GSS. These results suggest that the postsynaptic CN plays a role in the induction of LTP in the hippocampus of the rats.  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