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   17305篇
  免费   2234篇
  国内免费   8篇
  19547篇
  2021年   227篇
  2019年   178篇
  2018年   211篇
  2017年   183篇
  2016年   325篇
  2015年   514篇
  2014年   574篇
  2013年   696篇
  2012年   809篇
  2011年   882篇
  2010年   568篇
  2009年   531篇
  2008年   691篇
  2007年   677篇
  2006年   592篇
  2005年   613篇
  2004年   635篇
  2003年   582篇
  2002年   538篇
  2001年   514篇
  2000年   560篇
  1999年   470篇
  1998年   212篇
  1997年   217篇
  1996年   197篇
  1995年   202篇
  1994年   201篇
  1993年   183篇
  1992年   393篇
  1991年   389篇
  1990年   385篇
  1989年   344篇
  1988年   331篇
  1987年   301篇
  1986年   254篇
  1985年   274篇
  1984年   235篇
  1983年   229篇
  1982年   173篇
  1981年   174篇
  1980年   163篇
  1979年   245篇
  1978年   207篇
  1977年   190篇
  1976年   181篇
  1975年   184篇
  1974年   182篇
  1973年   205篇
  1972年   183篇
  1971年   171篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
12.
Neurotoxic Esterase in Human Nervous Tissue   总被引:1,自引:1,他引:0  
  相似文献   
13.
14.
A crown-of-thorns starfish control program was conducted at Grub Reef (central Great Barrier Reef) in an area (0.64 km2) which encompassed 53 individual patch reefs. During a two week period, 15 divers injected 3175 starfish with copper sulphate. The program was considered unsuccessful. Although starfish abundance had declined significantly after the control efforts, biological surveys indicated that a relatively large number of starfish remained. The surveys also indicated a general decline in the number of starfish along the reef perimeter, outside the control area. The total cost of the control program was $35 per starfish. These results have important implications for the implementation of future control programs and highlight the need to undertake before and after biological surveys to assess the effectiveness of the control efforts.  相似文献   
15.

Background  

Populations of the Oriental White-backed Vulture (Gyps bengalensis) have declined by over 95% within the past decade. This decline is largely due to incidental consumption of the non-steroidal anti-inflammatory veterinary pharmaceutical diclofenac, commonly used to treat domestic livestock. The conservation status of other Gyps vultures in southern Asia is also of immediate concern, given the lack of knowledge regarding status of their populations and the continuing existence of taxonomic uncertainties. In this study, we assess phylogenetic relationships for all recognized species and the majority of subspecies within the genus Gyps. The continuing veterinary use of diclofenac is an unknown but potential risk to related species with similar feeding habits to Gyps bengalensis. Therefore, an accurate assessment of the phylogenetic relationships among Gyps vultures should aid in their conservation by clarifying taxonomic uncertainties, and enabling inference of their respective relatedness to susceptible G. bengalensis.  相似文献   
16.
The salicylic acid derivative acetylsalicylic acid (ASA) was found to promote colony formation from protoplasts isolated from embryogenic suspension cultures of an elite maize inbred line. The drug was most effective at concentrations of 30–100 mg/l, and increases of more than 20-fold in the number of colonies recovered from protoplasts were obtained. The rate of growth of protoplast-derived cell colonies was not affected.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - DMSO dimethylsulfoxide - KM Kao and Michayluk medium (1975) - MES 2[N-morpholino]ethanesulfonic acid - ASA acetylsalicylic acid  相似文献   
17.
18.
19.
We have shown that affinity capillary electrophoresis (ACE) can be utilized to screen peptides that bind to the extracellular binding domain of the erythropoietin receptor (EBP). The comparison of the cyclic peptides GGTYSCHFGPLTWVCKPQGG (EMP1) GGTYSCHFGPLTAVCKPQGG (EMP13), and LGRKYSCHFGPLTWVCQPAKKD (EMP37) with the linear peptides HFGPLTWV (EMP26) and FMRF as ACE buffer additives were investigated. When EMP1 and EMP37 were the buffer additives, an abrupt change in the electrophoretic mobility of EBP was observed in the electropherogram. When EMP13, EMP26, and FMRF were examined under identical ACE conditions as EMP1 and EMP37, no significant change in the electrophoretic mobility of EBP was observed. These results correlate well with previously reported IC50 competitive binding data; that is, EMP1 and EMP37 bind to EBP while EMP13 and EMP26 bind very weakly. These observations strongly infer that peptide.EBP dimerization were induced by EMP1, and EMP37 but not by EMP13, EMP26 or FMRF. This ACE method provides a rapid tool for the detection of small peptides or drugs that bind to EBP.  相似文献   
20.
Recently, there has been increased interest in the influence of maternal prenatal nutrition on the course and outcome of pregnancy. Evidence has accumulated that a woman''s weight before pregnancy and the weight gained during pregnancy directly affect infant birth weight, incidence of neonatal mortality, and growth and development of the infant during the first year of life. Although recent recommendations for weight gain in pregnancy have been liberalized, a survey of 195 pregnant women who had prenatal visits in both clinic and private offices showed deficiencies in their understanding of the subject. Some 37 percent of women believed they should gain 20 pounds (9 kg) or less during pregnancy. Eight percent admitted to dieting before at least one antenatal visit and 54 percent thought their doctor would not be concerned about too little weight gained during pregnancy. This suggests that many women and some doctors are still ignorant of current concepts of proper nutrition during pregnancy. Apparently, increased lay and professional educational efforts are needed.  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