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   614731篇
  免费   69240篇
  国内免费   1600篇
  685571篇
  2018年   6272篇
  2017年   6030篇
  2016年   8173篇
  2015年   10383篇
  2014年   12457篇
  2013年   17552篇
  2012年   19627篇
  2011年   19881篇
  2010年   13353篇
  2009年   12363篇
  2008年   17062篇
  2007年   17585篇
  2006年   16490篇
  2005年   15744篇
  2004年   15512篇
  2003年   14851篇
  2002年   14432篇
  2001年   34006篇
  2000年   33879篇
  1999年   26290篇
  1998年   7877篇
  1997年   8517篇
  1996年   7837篇
  1995年   7213篇
  1994年   6872篇
  1993年   6851篇
  1992年   20228篇
  1991年   19323篇
  1990年   18378篇
  1989年   17896篇
  1988年   16405篇
  1987年   15044篇
  1986年   13984篇
  1985年   13706篇
  1984年   11090篇
  1983年   9361篇
  1982年   6922篇
  1981年   6134篇
  1980年   5798篇
  1979年   10253篇
  1978年   7866篇
  1977年   7190篇
  1976年   6441篇
  1975年   7140篇
  1974年   7663篇
  1973年   7483篇
  1972年   6787篇
  1971年   6184篇
  1970年   5362篇
  1969年   5010篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
132.
From three Fouquieria sp. 12 iridoid glucosides were isolated and identified. Eight of these were structurally related to galioside (monotropein methylester), while four were hydroxy substitution products of deoxyloganin. In three cases the glucoside occurred together with the corresponding 10-O-acetate.  相似文献   
133.
An indwelling nasal suction tampon is described that effectively controls both intraoperative and postoperative nasal hemorrhage. The significant benefits of this device are better intraoperative control for the surgeon and less complicated postoperative recovery. I do not have any financial involvement in this device, but I would like other nasal surgeons to benefit from its particular advantages. The device is available under the trade name Instant and may be obtained from Innovations by Westmed, 3351 E. Hemisphere Loop, Tucson, Ariz. 85706; (602) 294-7987.  相似文献   
134.
In many species of actinomycetes, carotenogenesis can be photoinduced. The capacity to respond to photoinduction is, however unstable and, in various strains of Streptomyces, is lost at a relatively high frequency. In Streptomyces setonii ISP5395, which normally produces no carotenoids, carotenoid-producing mutants can be obtained following protoplast regeneration. We report here the characterization of a gene, crtS, which was isolated from one such mutant and can confer on wild-type S. setonii ISP5395 cells the capacity to synthesize carotenoids. Sequence analysis of crtS reveals an open reading frame, which shows homology to genes that encode alternative sigma factors in Bacillus subtilis. We propose that crtS encodes a sigma factor which is necessary for the expression of a cryptic gene(s) for carotenoid biosynthesis in S. setonii ISP5395.  相似文献   
135.
136.
137.
138.
139.
140.
Convenient extraction and radioimmunoassay methods for measurement of leukotrienes C4 and D4 (LTC4 and LTD4) in biological fluids are described. LTC4 or LTD4 in plasma was extracted with acetonitrile, and the extract was washed with dichloromethane then adjusted to pH 3.5 or 6.0, respectively. Each leukotriene was partially purified by using a C18-bonded silica cartridge and quantitated by radioimmunoassay. Amounts of LTC4 and LTD4 in the range of 0.025-1.6 ng could be assayed in plasma. This procedure was employed to examine the increase in plasma LTC4 (0.249 +/- 0.036 ng/ml) and LTD4 (1.399 +/- 0.235 ng/ml) of guinea pigs during intravenous challenge-induced anaphylactic bronchoconstriction, and the suppression of the increase of bronchoconstriction and leukotrienes by the administration of 5-lipoxygenase inhibitors such as E6080 (6-hydroxy-2-(4-sulfamoylbenzyl-amino)- 4,5,7-trimethylbenzothiazole hydrochloride), AA861 (2,3,5-trimethyl-6-(12-hydroxy-5,10-dodecadiynyl)-1,4-benzoquinone ) and phenidone. On the other hand, LTC4 and LTD4 were not detected in plasma after an inhaled challenge, though significant bronchoconstriction was provoked. It was concluded that the present study validates a new technique for quantitating plasma leukotrienes on the basis of pH and a suitable method for evaluating the pharmacological efficacy of 5-lipoxygenase inhibitors.  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