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   9589篇
  免费   1230篇
  国内免费   1篇
  2021年   139篇
  2019年   114篇
  2018年   108篇
  2017年   104篇
  2016年   161篇
  2015年   283篇
  2014年   317篇
  2013年   412篇
  2012年   503篇
  2011年   492篇
  2010年   326篇
  2009年   312篇
  2008年   435篇
  2007年   404篇
  2006年   402篇
  2005年   324篇
  2004年   307篇
  2003年   271篇
  2002年   294篇
  2001年   275篇
  2000年   224篇
  1999年   187篇
  1998年   107篇
  1997年   121篇
  1996年   112篇
  1995年   97篇
  1994年   92篇
  1993年   108篇
  1992年   181篇
  1991年   158篇
  1990年   163篇
  1989年   178篇
  1988年   159篇
  1987年   147篇
  1986年   125篇
  1985年   172篇
  1984年   144篇
  1983年   117篇
  1982年   133篇
  1981年   163篇
  1980年   133篇
  1979年   120篇
  1978年   88篇
  1977年   93篇
  1976年   105篇
  1974年   91篇
  1973年   83篇
  1972年   92篇
  1971年   87篇
  1969年   88篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
The ultrasonic calls produced by three day old mice when separated from the nest mother and siblings increase in number when naloxone is injected.  相似文献   
5.
1. Male Japanese quail were given 2.20 x 10(-4)-14.53 mg uranium/kg intravenously as uranyl ion (235U label). 2. The relationship between dosage and the 18-hr accumulation of U in leg bones, liver, kidneys and testes was linear. 3. Increases in U deposition with increased dosage were approximately 1:1, except for kidneys where 10-fold increases in dosage resulted in 25-fold increases in deposition. 4. Estradiol-17 beta increased U deposition in bones by 15-fold thereby providing some protection for the kidneys as now the ratio of dosage to accumulation was 1:1.  相似文献   
6.
Calcium efflux and EGTA-induced calcium release from an internal platelet membrane fraction have been studied after the oxalate-supported calcium uptake had reached steady state. Increasing external calcium concentrations stimulate the calcium efflux velocity, with an apparent half-maximal stimulation at about 5 microM outside calcium concentration and a maximal velocity of calcium efflux of 4.66 +/- 2.32 nmol X min-1 X mg-1. Moreover, the ratio of the liberated calcium on the loaded calcium seems to be independent of the increasing external calcium concentration. Increasing the calculated internal calcium concentration by varying the oxalate potassium concentration from 10 mM to 1 mM results in an increase of the liberated calcium from the membrane vesicles from 7.4% to 63%, respectively, without changing the calcium efflux velocity. Similar conclusions can be drawn from the observation of results from the calcium efflux and EGTA-induced calcium release methods. Moreover, calcium pump reversal does not seem to be responsible for the calcium efflux or calcium release. All these different points added to the previously described regulation of calcium efflux by the catalytic subunit of cAMP protein kinase suggest us that the mechanism of calcium liberation by the platelet membranes is different from the calcium uptake.  相似文献   
7.
8.
9.
The investigation of Encelia canescens afforded, in addition to several known compounds, four new dimeric p-hydroxyacetophenone derivatives, two epimeric chromene dimers and two epimeric mixed dimers of euparin and encecalin. Furthermore, derivatives of tremetone and of encecalin were present. The structures were elucidated hy high field 1H NMR spectroscopy.  相似文献   
10.
Abstract The effectiveness of immunofluorescence flow cytometry and cell sorting to detect, quantify and separate indigenous bacterial populations present in low concentrations in sewage outflow was investigated. Preparatory experiments for targeted recovery revealed indigenous, immunoglobulin-G-binding particles present at low levels in sewage outflow samples taken from Coniston Water. Fluorescence-activated cell sorting of this population was employed to enrich for these particles, which were confirmed as bacterial cells. This cell population comprised approximately 23% of the total plate count on MacConkey agar before cell sorting, rising to approximately 95% after sorting. These results corresponded to cell densities of less than 5% of the total plate count on R2A agar. Taxonomic tests suggested the bacterium to be Ochrobactrum anthropi .  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