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   13550篇
  免费   1242篇
  国内免费   3篇
  2021年   156篇
  2020年   116篇
  2019年   118篇
  2018年   148篇
  2017年   157篇
  2016年   248篇
  2015年   399篇
  2014年   482篇
  2013年   648篇
  2012年   807篇
  2011年   710篇
  2010年   521篇
  2009年   449篇
  2008年   648篇
  2007年   703篇
  2006年   649篇
  2005年   605篇
  2004年   640篇
  2003年   602篇
  2002年   611篇
  2001年   262篇
  2000年   250篇
  1999年   270篇
  1998年   202篇
  1997年   178篇
  1996年   142篇
  1995年   172篇
  1994年   176篇
  1993年   143篇
  1992年   213篇
  1991年   197篇
  1990年   159篇
  1989年   162篇
  1988年   155篇
  1987年   161篇
  1986年   146篇
  1985年   141篇
  1984年   148篇
  1983年   116篇
  1982年   154篇
  1981年   132篇
  1980年   101篇
  1979年   117篇
  1978年   119篇
  1977年   95篇
  1976年   91篇
  1975年   107篇
  1974年   107篇
  1973年   89篇
  1972年   79篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Nine schizophrenic patients participated in a study which explored whether EEG feedback techniques could effect changes in the EEG similar to those associated with neuroleptic-induced improvement. During five sessions, each patient was presented feedback signals which continuously refected the discrepancy between characteristics of the patient's EEG power spectral profile and spectral profile characteristics associated by past research with neuroleptic induced clinical improvement. Significant within-session changes were observed for two of three EEG power spectrum bands of interest. No significant session-to-session EEG changes were observed. The results suggest that the EEG of schizophrenics can be temporarily altered, using feedback techniques, in a way that mimics the EEG changes that have been shown to occur with neuroleptic induced clinical improvement.The authors are indebted to Turan M. Itil, John W. Fredrickson, Michael Madwed, and Irene B. Francis. Senior authorship is shared equally.  相似文献   
22.
Seventy-two Schiffs bases, 44 corresponding secondary amines, and 12 N-acetylated compounds were tested on their growth activity. Eighty-one compounds were active as growth inhibitors in at least one of three bioassays.  相似文献   
23.
24.
25.
26.
27.
Bedbugs     
  相似文献   
28.
The polypeptide composition of the large and small subunits of Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) from Arabidopsis thaliana, A. suecica and Cardaminopsis arenosa have been studied by IEF (isoelectric focusing) analysis. The putative recent alopolyploid origin of A. suecica is supported. The chloroplast encoded large subunits served to identify solely A. thaliana as the maternal parent whereas the nuclear encoded small subunits indicate C. arenosa as the paternal species.  相似文献   
29.
The inactivation of Bacillus subtilis spores during long-term exposure (up to several months) to extreme dryness (especially vacuum) is strain-dependent, through only to a small degree. During a first phase (lasting about four days) monolayers of spores lose about 20% of their viability, regardless of the strain studied. During this phase loss in viability can be equally attributed both to damages of hydrophobic structures (membranes and proteins) and DNA. During a second phase lasting for the remaining time of experimental observation (weeks, months and years) the loss in viability is slowed. A viability of 55% to 75% (depending on the strain) is attained after a total exposure of 36 days. The loss in viability during the second phase can be correlated with the occurrence of DNA double strand breaks. Also covalent DNA-protein cross-links are formed by vacuum exposure. If the protein moiety of these cross-links is degraded by proteinase K-treatment in vitro additional DNA double strand breaks result. The data are also discussed with respect to survival on Mars and in near Earth orbits.  相似文献   
30.
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