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   175372篇
  免费   11391篇
  国内免费   22篇
  186785篇
  2023年   901篇
  2021年   1815篇
  2020年   1651篇
  2019年   1730篇
  2018年   4293篇
  2017年   3828篇
  2016年   5324篇
  2015年   7545篇
  2014年   7776篇
  2013年   10387篇
  2012年   12331篇
  2011年   11303篇
  2010年   7353篇
  2009年   5511篇
  2008年   9319篇
  2007年   9070篇
  2006年   8571篇
  2005年   7686篇
  2004年   7386篇
  2003年   6752篇
  2002年   6216篇
  2001年   3913篇
  2000年   3796篇
  1999年   3147篇
  1998年   1348篇
  1997年   1044篇
  1996年   1006篇
  1995年   984篇
  1994年   948篇
  1992年   2077篇
  1991年   1911篇
  1990年   1791篇
  1989年   1776篇
  1988年   1557篇
  1987年   1456篇
  1986年   1340篇
  1985年   1445篇
  1984年   1246篇
  1983年   1065篇
  1982年   869篇
  1979年   1191篇
  1978年   892篇
  1977年   850篇
  1975年   983篇
  1974年   1039篇
  1973年   1015篇
  1972年   859篇
  1970年   825篇
  1969年   874篇
  1968年   811篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
In this paper we quantify and characterize the expression of recombinant beta-lactoglobulin (rBLG) in prokaryote and eukaryote cells. In Escherichia coli we used the pET26 vector, which permits the secretion of rBLG in periplasm. We studied the expression of rBLG in COS-7 cells and in vivo in mouse tibialis muscle. The expression of rBLG was measured by two immunoassays specific, respectively, for BLG in its native and denatured conformation. We observed that rBLG was essentially expressed in a denatured form in E. coli even in the periplasm, whereas rBLG in eukaryote cells was found in its native conformation.  相似文献   
13.
The enzyme 6-phosphogluconate dehydrogenase (6-phospho-D-gluconate: NADP+ oxidoreductase, decarboxylating EC 1.1.1.44) from bass liver has been purified to over 95% of homogeneity by gel filtration, affinity and ion exchange chromatographies. The apparent molecular weight was estimated by gel filtration chromatography to about 100,000. Analysis of the enzyme on sodium dodecyl sulphate polyacrylamide gel electrophoresis showed to be a dimeric protein. The effect of pH and kinetic properties were studied.  相似文献   
14.
A new internal perfusion method has been developed which allows control of the internal solute composition in squid axons. The superiority of this technique compared to the old perfusion methods is shown by the experiments performed which have reproduced, both qualitatively and quantitatively, the Na+ and Ca2+ fluxes observed in intact and dialyzed axons. Compared with the internal dialysis, the perfusion method has the advantage that the permeability barrier give by the porous capillary has been eliminated. This allows the introduction into the axon of solutes with very high molecular weight, at the same time that a fast and reliable internal control can be achieved.  相似文献   
15.
Administration of purified pertussis toxin to rats induced persistent tachycardia, (observed in conscious rats but not after pithing); as little as 0.05 microgram/100 g produced a significant effect. Pertussis toxin-treatment did not affected the pressor response produced in the pithed rats by the alpha 2-adrenergic agonist methoxamine but markedly diminished the pressor effect of the alpha 2-adrenergic agonists clonidine and azepexole. A role of adenylate cyclase inhibition in the action of postsynaptic vascular alpha 2-adrenergic receptors is suggested.  相似文献   
16.
The aim of this study was to design a new antisense oligonucleotide (ON) carrier system based on alginate nanoparticles and to investigate its ability to protect ON from degradation in the presence of serum. Pharmacokinetics and tissue distribution of ON-loaded nanoparticles have been determined after intravenous administration. An original and dynamic process for ON loading into polymeric nanoparticles has been applied. It is based on the diffusion of ON or ON/polylysine complex into the nanoparticle or the alginate gel, respectively. Indeed, the single coincubation of ON with nanoparticles led, within a few days, to an extremely efficient association. The diffusion kinetic of ON was shown to be dependent on several parameters, incubation temperature, ON concentration, presence or absence of polylysine, polylysine molecular weight, and nanoparticle preparation procedure. This new alginate-based system was found to be able to protect [33P]-radiolabeled ON from degradation in bovine serum medium and to modify their biodistribution, as an important accumulation of radioactivity was observed in the lungs, in the liver, and in the spleen after intravenous administration into mice. ON may be associated efficiently with calcium alginate in a colloidal state. Such nanosponges are promising carriers for specific delivery of ON to lungs, liver, and spleen.  相似文献   
17.
The relations between the saccus lacrimalis and different portions of the musculus orbicularis oculi were studied in orbital regions of human fetuses sectioned into numbered series. No insertions of the pars lacrimalis or Horner's muscle on the saccus were found. These muscular fibres pass along the dorsal wall of the saccus and are separated from it by the reflex tendon of the ligamentum palpebrale mediale. The only muscular fibres that insert on the saccus are those that approach the anterior face of the saccus and the fornix. The fibres that insert on the anterior face proceed from the deep bundles of the pars preseptalis of the lower eyelids, and those that insert on the fornix derive from the deep bundles of the pars preseptalis of the upper eyelid.  相似文献   
18.
Summary Eicosapentaenoic acid (EPA) volumetric productivity from an outdoor chemostat culture ofPhaeodactylum tricornutum UTEX 640 in a 50-l tubular photobioreactor varies with dilution rate, reaching a maximum of 47.8 mg l–1 d–1 at D=0.36 d–1. Continuous culture at high dilution rates' is proposed as the most adequate operating mode to maximize polyunsaturated fatty acid production.  相似文献   
19.
20.
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