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   18678篇
  免费   1372篇
  国内免费   5篇
  20055篇
  2021年   128篇
  2020年   110篇
  2019年   115篇
  2018年   292篇
  2017年   259篇
  2016年   446篇
  2015年   776篇
  2014年   724篇
  2013年   1054篇
  2012年   1281篇
  2011年   1247篇
  2010年   750篇
  2009年   593篇
  2008年   1103篇
  2007年   1107篇
  2006年   1057篇
  2005年   1002篇
  2004年   928篇
  2003年   855篇
  2002年   812篇
  2001年   406篇
  2000年   437篇
  1999年   393篇
  1998年   188篇
  1997年   146篇
  1996年   137篇
  1995年   140篇
  1994年   140篇
  1993年   115篇
  1992年   240篇
  1991年   235篇
  1990年   219篇
  1989年   170篇
  1988年   183篇
  1987年   158篇
  1986年   145篇
  1985年   134篇
  1984年   119篇
  1983年   96篇
  1982年   93篇
  1981年   120篇
  1980年   89篇
  1979年   118篇
  1978年   106篇
  1977年   87篇
  1976年   100篇
  1975年   79篇
  1974年   97篇
  1973年   70篇
  1971年   82篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
The secondary structures of cow and sheep kappa-caseins were established according to the predictive rules of Chou and Fasman. The diagrams derived from this treatment allowed us to study the chymosin sensitive bond (milk-clotting process), as well as the glycosylation and phosphorylation sites, found to be situated in beta-turns. Despite a high variability between the primary structures of the COOH-terminal part (caseinoglycopeptide) of cow, sheep, and also other caseins, the secondary structures of the biologically important sites were found to be conserved.  相似文献   
102.
103.
The NADH: nitrate reductase from durum wheat leaves was inactivated by cyanide and its activity restored by thiosulphate and beef kidney rhodanese. Rhodanese and thiosulphate, added to NADH-nitrate reductase before cyanide treatment protected NADH-nitrate reductase activity. No oxidizing agent was required for the protection or restoration of cyanide treated NADH-nitrate reductase.  相似文献   
104.
VO2 max, maximum oxygen uptake, has been measured in 4 normal young men, before and after beta-adrenergic blockade (0.5 to 5 mg Pindolol by mouth). Pindolol induces bradycardia and reduces VO2 max. A statistically significant positive correlation appears between posology of Pindolol and bradycardia, this posology and reduction of VO2 max, and finally between bradycardia and reduction of VO2 max. These correlations indicate that the reduction of VO2 max is best explained by a circulatory limitation of oxygen supply to active muscles.  相似文献   
105.
A method for electrophoretic detection of NAD(P)+ase solubilized from red cell membranes is described. The method reveals both NAD+ase and NADP+ase and can be applied to a screening procedure for the detection of electrophoretic variants. The initial chracterization of the solubilized enzyme is also described.  相似文献   
106.
107.
108.
109.
The fraction of cases reported, known as ‘reporting’, is a key performance indicator in an outbreak response, and an essential factor to consider when modelling epidemics and assessing their impact on populations. Unfortunately, its estimation is inherently difficult, as it relates to the part of an epidemic which is, by definition, not observed. We introduce a simple statistical method for estimating reporting, initially developed for the response to Ebola in Eastern Democratic Republic of the Congo (DRC), 2018–2020. This approach uses transmission chain data typically gathered through case investigation and contact tracing, and uses the proportion of investigated cases with a known, reported infector as a proxy for reporting. Using simulated epidemics, we study how this method performs for different outbreak sizes and reporting levels. Results suggest that our method has low bias, reasonable precision, and despite sub-optimal coverage, usually provides estimates within close range (5–10%) of the true value. Being fast and simple, this method could be useful for estimating reporting in real-time in settings where person-to-person transmission is the main driver of the epidemic, and where case investigation is routinely performed as part of surveillance and contact tracing activities.  相似文献   
110.
These tables list both published and a number of unpublished mutations in genes associated with early onset defects in mitochondrial DNA (mtDNA) maintenance including C10orf2, SUCLG1, SUCLA2, TYMP, RRM2B, MPV17, DGUOK and TK2. The list should not be taken as evidence that any particular mutation is pathogenic. We have included genes known to cause mtDNA depletion, excluding POLG1, because of the existing database (http://tools.niehs.nih.gov/polg/). We have also excluded mutations in C10orf2 associated with dominant adult onset disorders.  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