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   311921篇
  免费   36146篇
  国内免费   161篇
  348228篇
  2018年   2733篇
  2017年   2564篇
  2016年   3580篇
  2015年   4856篇
  2014年   5831篇
  2013年   7804篇
  2012年   9147篇
  2011年   9280篇
  2010年   6100篇
  2009年   5891篇
  2008年   8273篇
  2007年   8448篇
  2006年   8197篇
  2005年   7984篇
  2004年   7749篇
  2003年   7514篇
  2002年   7312篇
  2001年   17490篇
  2000年   17644篇
  1999年   13548篇
  1998年   4108篇
  1997年   4302篇
  1996年   4007篇
  1995年   3609篇
  1994年   3604篇
  1993年   3675篇
  1992年   10529篇
  1991年   10438篇
  1990年   9974篇
  1989年   9777篇
  1988年   9109篇
  1987年   8476篇
  1986年   7644篇
  1985年   7522篇
  1984年   5942篇
  1983年   5155篇
  1982年   3706篇
  1981年   3261篇
  1980年   3105篇
  1979年   5428篇
  1978年   4169篇
  1977年   3804篇
  1976年   3353篇
  1975年   3803篇
  1974年   3998篇
  1973年   3921篇
  1972年   3444篇
  1971年   3217篇
  1970年   2849篇
  1969年   2761篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
A rapid, simple and sensitive reversed-phase high-performance liquid chromatographic (HPLC) method has been developed for the measurement of acyclovir concentrations in human plasma and its use in bioavailability studies is evaluated. Unchanged acyclovir has been quantified without the introduction of an internal standard using the present method. Human plasma proteins were selectively precipitated by the addition of 7% perchloric acid to spiked plasma samples or to the plasma samples obtained after acyclovir administration to human volunteers and the mixture was spun at 1000 g for 10 min. The supernatant was directly injected into a Novaflex C18 column and detected at 254 nm. The mobile phase consisted of octane sulfonic acid buffer (pH 2.5) and methanol (92:08). The limit of quantitation for acyclovir in plasma was 20 ng/ml, which enabled the determination of the area under the curve (AUC) more precisely, that is, it is much closer to its extrapolated value. The present method has been successfully applied to samples from bioavailability studies.  相似文献   
52.
Venous ulcers.     
S. J. Fratesi  T. K. Scobie 《CMAJ》1982,126(6):631-635
  相似文献   
53.
Experiments on frogs were performed to examine the effect of the M-cholinomimetic pilocarpine on the heart. It was discovered that at concentrations of 10(-15)--10(-5) g/ml pilocarpine exerted only an adverse chronotropic effect on the perfused heart. When applied at a concentration of 10(-4) g/ml the drug produced a negative as well as a positive chronotropic effect. The latter occurred spasmodically (without progressive rise in the heart rate) in association with a slow heart rate. In some experiments such effects were preceded by a certain deceleration of the heart. In experiments with positive chronotropic effects, arrhythmias and sinoatrial dissociation were observed sometimes. Experiments with recording of the electrograms of the sinuses and lower parts showed that such effects were caused not by pacemaker acceleration but by the removal of the blockade of conduction, between the pacemaker and the atria. As far as the pacemaker is concerned, pilocarpine exerted only a negative chronotropic effect.  相似文献   
54.
55.
Casualties.     
  相似文献   
56.
57.
58.
59.
The ability of human uterine endometrium to aromatize androstenedione to estrogens was investigated using 10 normal and neoplastic tissues. Normal and neoplastic endometrial homogenates were incubated with [6,7-3H]androstenedione (A) and NADPH. Estrone (E1) and estradiol (E2) were subsequently isolated in amounts ranging from 0-17600 fmol/h/g and 0-377 fmol/h/g, respectively, from the incubates after purifications by using Bio-Rad AG1-X2 column, thin layer chromatographies and co-crystallization. The conversion of A to E1 and E2 was significantly higher in neoplastic tissues.  相似文献   
60.
Colchicine-binding protein (CBP) was purified from a cultured carrot cell extract by DEAE-Sephacel, phosphocellulose and Sephadex G200 column chromatographies. The purified CBP separated into three bands on SDS-polyacrylamide gel electrophoresis. One of them reacted with a monoclonal antibody against chick brain alpha-tubulin and the other two with that against beta-tubulin. Colchicine-binding activity of the purified protein was enhanced by tartrate and inhibited little by an excess of podophyllotoxin. It decayed following first order kinetics, but was more stable than the CBP in the crude extract. The binding constant of the purified CBP for colchicine was 0.57 microM-1 and the number of binding sites of colchicine per mg protein was about 2 nmol. This binding constant is about ten times lower than that of porcine brain tubulin under identical conditions.  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