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   26103篇
  免费   81篇
  国内免费   100篇
系统科学   162篇
丛书文集   180篇
教育与普及   48篇
理论与方法论   85篇
现状及发展   10738篇
研究方法   1113篇
综合类   13538篇
自然研究   420篇
  2013年   215篇
  2012年   385篇
  2011年   773篇
  2010年   161篇
  2008年   416篇
  2007年   533篇
  2006年   517篇
  2005年   487篇
  2004年   455篇
  2003年   438篇
  2002年   480篇
  2001年   975篇
  2000年   953篇
  1999年   559篇
  1992年   526篇
  1991年   419篇
  1990年   462篇
  1989年   470篇
  1988年   438篇
  1987年   446篇
  1986年   436篇
  1985年   512篇
  1984年   462篇
  1983年   383篇
  1982年   358篇
  1981年   342篇
  1980年   360篇
  1979年   838篇
  1978年   682篇
  1977年   577篇
  1976年   549篇
  1975年   560篇
  1974年   726篇
  1973年   555篇
  1972年   594篇
  1971年   752篇
  1970年   920篇
  1969年   644篇
  1968年   717篇
  1967年   623篇
  1966年   602篇
  1965年   422篇
  1964年   130篇
  1959年   210篇
  1958年   380篇
  1957年   252篇
  1956年   197篇
  1955年   186篇
  1954年   182篇
  1948年   150篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
11.
Deposition of amyloid β-protein (Aβ) in the brain is an early and invariant neuropathological feature of Alzheimer’s disease (AD). The current search for anti-AD drugs is mainly focused on modification of the process of accumulation of Aβ in the brain. Here, we review four anti-amyloidogenic strategies: (i) reduction of Aβ production, which has mainly been approached with secretase inhibition, (ii) promotion of the Aβ degrading catabolic pathway, including an Aβ degrading enzyme, neprilysin, (iii) immunotherapy for Aβ and (iv) inhibition of Aβ aggregation. We have reported that AD patients have a favorable molecular environment for Aβ aggregation and that various compounds, such as polyphenols, interfere with Aβ aggregation and destabilize preformed Aβ fibrils. Received 21 December 2005; received after revision 14 February 2006; accepted 29 March 2006  相似文献   
12.
    
Summary The inducing factor of mating tube formation ofRhodosporidium turuloides, named rhodotorucine A (H-Tyr-Pro-Glu-Ile-Ser-Trp-Thr-Arg-Asn-Gly-Cys(S-farnesyl)-OH), has been synthesized to confirm the structure proposed for the natural lipopeptide. The synthetic S-farnesyl undecapeptide has identical Rf values on TLC using several different solvents, and also the same biological activity as the natural hormone.Acknowledgments. We wish to express our thanks to Drs E. Ohmura, M. Nishikawa and M. Yoneda of Takeda Chemical Industries and Dr I. Banno of Institute for Fermentation, Osaka, for their encouragement throughout this work.  相似文献   
13.
14.
15.
Summary Significant decreases in the levels of both carbonic anhydrase type B and total esterase activity of human erythrocytes were observed after physical exercise (bicycle ergometer, 150 W for 30 min). Since carbonic anhydrase B-dependent esterase activity likewise decreased, the decrease in the total esterase activity would be caused by the decrease of carbonic anhydrase B activity. The specific activity of carbonic anhydrase B tended to decrease after the exercise. On the other hand no such effects were noted for carbonic anhydrase type C.  相似文献   
16.
17.
  总被引:6,自引:0,他引:6  
  相似文献   
18.
The mechanism of the positive inotropic effect of prostacyclin (PGI2) (2.6×10?6 mol/l) on the isolated right ventricle of rat heart was studied. Our results show that the positive inotropic effect of prostacyclin is produced indirectly through beta adrenoceptors and slow Ca2+ channels, because blockade of slow Ca2+ channels with verapamil (10?6 mol/l) and beta adrenoceptors with propranolol (10?6 mol/l) abolishes this effect. Alpha adrenoceptors do not mediate the action of PGI2.  相似文献   
19.
This paper defines a new class of generalized type I functions, and obtains Kuhn-Tucker necessary and sufficient conditions and duality results for constrained optimization problems in the presence of the aforesaid weaker assumptions on the objective and constraint functions involved in the problem.  相似文献   
20.
Heterosexual chemoattraction studies on juvenile worms showed that 20- and 21-day-old worms do not attract each other, whereas 23- and 28-day-old worms are attracted to each other and pair with worms of the opposite sex. This onset of chemoattraction in vitro corresponds to the time when worms begin pairing in vivo. The ability of single worms to locate each other and mate is presumably mediated by chemoreceptors.  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