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   113451篇
  免费   21676篇
  国内免费   7103篇
  2024年   227篇
  2023年   1177篇
  2022年   2663篇
  2021年   4639篇
  2020年   4838篇
  2019年   6941篇
  2018年   6763篇
  2017年   6300篇
  2016年   7437篇
  2015年   9139篇
  2014年   9837篇
  2013年   10557篇
  2012年   9770篇
  2011年   8789篇
  2010年   7294篇
  2009年   5676篇
  2008年   5361篇
  2007年   4449篇
  2006年   3958篇
  2005年   3371篇
  2004年   2899篇
  2003年   2629篇
  2002年   2229篇
  2001年   1896篇
  2000年   1747篇
  1999年   1513篇
  1998年   840篇
  1997年   772篇
  1996年   782篇
  1995年   676篇
  1994年   688篇
  1993年   514篇
  1992年   781篇
  1991年   623篇
  1990年   538篇
  1989年   498篇
  1988年   408篇
  1987年   350篇
  1986年   323篇
  1985年   307篇
  1984年   256篇
  1983年   224篇
  1982年   171篇
  1981年   100篇
  1980年   112篇
  1979年   140篇
  1978年   103篇
  1976年   111篇
  1974年   126篇
  1972年   107篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
63.
Yang  Su-Rong  Sun  Huan-Xin  Hu  Zhen-Zhen  Wang  Si-Heng  Sun  Hui  Xue  Yin-Jia  Ye  Chen-Bo 《Sleep and biological rhythms》2017,15(1):57-65
Sleep and Biological Rhythms - Chronic sleep deprivation (SD) is an overwhelming problem in young students. Firstly, we investigated whether different levels of pre-training SD had effects on...  相似文献   
64.
Applied Microbiology and Biotechnology - The objective of this study was to identify and exploit a robust biocatalyst that can be applied in reductive amination for enantioselective synthesis of...  相似文献   
65.
Purification of (Ca2+-Mg2+)-ATPase from rat liver plasma membranes   总被引:1,自引:0,他引:1  
The Ca2+-stimulated, Mg2+-dependent ATPase from rat liver plasma membranes was solubilized using the detergent polyoxyethylene 9 lauryl ether and purified by column chromatography using Polybuffer Exchanger 94, concanavalin A-Sepharose 4B, and Sephadex G-200. The molecular weight of the enzyme, estimated by gel filtration in the presence of the detergent on a Sephadex G-200 column, was 200,000 +/- 15,000. The enzyme was purified at least 300-fold from rat liver plasma membranes and had a specific activity of 19.7 mumol/mg/min. Polyacrylamide gel electrophoresis under nondenaturing conditions of the purified enzyme indicated that the enzymatic activity correlated with the major protein band. In sodium dodecyl sulfate-polyacrylamide gel electrophoresis, one major band in the molecular weight range of 70,000 +/- 5,000 was seen. The isoelectric point of the purified enzyme was 6.9 +/- 0.2 as determined by analytical isoelectric focusing. The enzyme was activated by Ca2+ with an apparent half-saturation constant of 87 +/- 2 nM for Ca2+. Calmodulin and trifluoperazine at the concentration of 1 microgram/ml and 100 microM, respectively, had no effect on the enzymatic activity.  相似文献   
66.
67.
68.
69.
70.
During the past 40 years, more than 400 Sudden Unexplained Deaths (SUDs) have occurred in Yunnan, southwestern China. Epidemiological and toxicological analyses suggested that a newly discovered mushroom called Trogia venenata was the leading culprit for SUDs. At present, relatively little is known about the genetics and natural history of this mushroom. In this study, we analyzed the sequence variation at four DNA fragments among 232 fruiting bodies of T. venenata collected from seven locations. Our ITS sequence analyses confirmed that all the isolates belonged to the same species. The widespread presence of sequence heterozygosity within many strains at each of three protein-coding genes suggested that the fruiting bodies were diploid, dikaryotic or heterokaryotic. Within individual geographic populations, we found significant deviations of genotype frequencies from Hardy-Weinberg expectations, with the overall observed heterozygosity lower than that expected under random mating, consistent with prevalent inbreeding within local populations. The geographic populations were overall genetically differentiated. Interestingly, while a positive correlation was found between population genetic distance and geographic distance, there was little correlation between genetic distance and barium concentration difference for the geographic populations. Our results suggest frequent inbreeding, geographic structuring, and limited gene flow among geographic populations of T. venenata from southwestern China.  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