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   35584篇
  免费   122篇
  国内免费   135篇
系统科学   186篇
丛书文集   478篇
教育与普及   74篇
理论与方法论   157篇
现状及发展   15472篇
研究方法   1464篇
综合类   17305篇
自然研究   705篇
  2013年   271篇
  2012年   508篇
  2011年   1236篇
  2010年   227篇
  2008年   602篇
  2007年   714篇
  2006年   665篇
  2005年   704篇
  2004年   789篇
  2003年   642篇
  2002年   679篇
  2001年   1021篇
  2000年   1005篇
  1999年   693篇
  1992年   659篇
  1991年   494篇
  1990年   529篇
  1989年   529篇
  1988年   513篇
  1987年   528篇
  1986年   566篇
  1985年   738篇
  1984年   527篇
  1983年   429篇
  1982年   384篇
  1981年   400篇
  1980年   472篇
  1979年   1119篇
  1978年   873篇
  1977年   835篇
  1976年   692篇
  1975年   691篇
  1974年   1001篇
  1973年   865篇
  1972年   884篇
  1971年   1019篇
  1970年   1422篇
  1969年   1093篇
  1968年   954篇
  1967年   994篇
  1966年   984篇
  1965年   700篇
  1964年   255篇
  1959年   355篇
  1958年   681篇
  1957年   454篇
  1956年   381篇
  1955年   335篇
  1954年   362篇
  1948年   293篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
大型仪器设备是高校开展教学、科研的物质保证,是高校实验室的主要技术装备,衡量一所高校办学实力和水平的重要指标之一.……  相似文献   
32.
Studies of intracellular traffic in yeast and mammalian systems have implicated members of the Rab family of small GTP-binding proteins as regulators of membrane fusion. We have used the patch clamp technique to measure exocytotic fusion events directly and investigate the role of GTP-binding proteins in regulating exocytosis in mast cells. Intracellular perfusion of mast cells with GTP-gamma S is sufficient to trigger complete exocytotic degranulation in the absence of other intracellular messengers. Here we show that GTP is a potent inhibitor of GTP-gamma S-induced degranulation, indicating that sustained activation of a GTP-binding protein is sufficient for membrane fusion. We have found that synthetic oligopeptides, corresponding to part of the effector domain of Rab3a, stimulate complete exocytotic degranulation, similar to that induced by GTP-gamma S. The response is selective for Rab3a sequence and is strictly dependent on Mg2+ and ATP. This suggests that sustained activation of a Rab3 protein causes exocytotic fusion. The peptide response can be accelerated by GDP-beta S, suggesting that Rab3a peptides compete with endogenous Rab3 proteins for a binding site on a target effector protein, which causes fusion on activation.  相似文献   
33.
34.
S J Weintraub  C A Prater  D C Dean 《Nature》1992,358(6383):259-261
  相似文献   
35.
36.
Summary Hydrochlorothiazide, acutely injected in rats, has a weak analgesic activity per se and potentiates and prolongs the antinociceptive effect of morphine.This work was supported in part by grants from Consiglio Nazionale delle Ricerche, and by Ministero della Pubblica Istruzione, Roma.  相似文献   
37.
38.
1 Results This paper presents the development of platinum nanocomposites structures based on organically modified c.a.2 nm core platinum nanoparticles.The chemical modification of the 4-mercaptoaniline functionalized particles by various in coming molecules is evidenced and precisely quantified.The particles can be dissolved like molecules in various solvents depending on the features of the new crown and X-rays shows that the interparticle distance is affected by the crown modification.These platinum n...  相似文献   
39.
煤矸石空心砖是一种新型环保墙体材料,符合国家及山西省出台的限制生产和使用实心黏土砖,鼓励发展新型建筑材料的政策。利用煤矸石制造的空心砖可以作为保温材料,既可节约建筑能耗,又可节约土地资源,减少环境污染。煤矸石空心砖同黏土实心砖相比,具有高强、轻质、隔音、隔热、保温、防震等优点,市场前景良好。  相似文献   
40.
This paper assesses the information content of two survey indicators for consumption developments in the near future for eight European countries in the period 1985–1998. Empirical work on this topic typically focuses on consumer confidence, the perceptions of buyers of consumption goods. This paper examines whether perceptions of sellers of consumption goods, measured by retail trade surveys, may also improve short‐term monitoring of consumption. We find that both consumer confidence and retailer confidence embody valuable information, when analysed in isolation. For France, Italy and Spain we conclude that adding retail confidence does not improve the indicator model once consumer confidence has been included. For the UK the reverse case is obtained. For the remaining four countries we show that combining consumer sentiment and retail trade confidence into a composite indicator leads to optimal results. Our results suggest that incorporating information from retail trade surveys may offer significant benefits for the analysis of short‐term prospects of consumption. Copyright © 2004 John Wiley & Sons, Ltd.  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