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   23378篇
  免费   697篇
  国内免费   87篇
系统科学   1134篇
丛书文集   121篇
教育与普及   45篇
理论与方法论   326篇
现状及发展   8594篇
研究方法   865篇
综合类   12877篇
自然研究   200篇
  2018年   756篇
  2017年   778篇
  2016年   513篇
  2013年   148篇
  2012年   537篇
  2011年   1398篇
  2010年   931篇
  2009年   568篇
  2008年   849篇
  2007年   1309篇
  2006年   396篇
  2005年   426篇
  2004年   467篇
  2003年   575篇
  2002年   417篇
  2001年   689篇
  2000年   677篇
  1999年   413篇
  1994年   321篇
  1992年   385篇
  1991年   276篇
  1990年   332篇
  1989年   291篇
  1988年   254篇
  1987年   314篇
  1986年   314篇
  1985年   386篇
  1984年   281篇
  1983年   264篇
  1982年   247篇
  1981年   227篇
  1980年   217篇
  1979年   597篇
  1978年   436篇
  1977年   403篇
  1976年   351篇
  1975年   357篇
  1974年   434篇
  1973年   395篇
  1972年   353篇
  1971年   419篇
  1970年   571篇
  1969年   436篇
  1968年   446篇
  1967年   415篇
  1966年   383篇
  1965年   287篇
  1958年   242篇
  1957年   155篇
  1956年   154篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
11.
G protein-coupled receptor (GPCR) signalling is mediated through transactivation-independent signalling pathways or the transactivation of protein tyrosine kinase receptors and the recently reported activation of the serine/threonine kinase receptors, most notably the transforming growth factor-β receptor family. Since the original observation of GPCR transactivation of protein tyrosine kinase receptors, there has been considerable work on the mechanism of transactivation and several pathways are prominent. These pathways include the “triple membrane bypass” pathway and the generation of reactive oxygen species. The recent recognition of GPCR transactivation of serine/threonine kinase receptors enormously broadens the GPCR signalling paradigm. It may be predicted that the transactivation of serine/threonine kinase receptors would have mechanistic similarities with transactivation of tyrosine kinase pathways; however, initial studies suggest that these two transactivation pathways are mechanistically distinct. Important questions are the relative importance of tyrosine and serine/threonine transactivation pathways, the contribution of transactivation to overall GPCR signalling, mechanisms of transactivation and the range of cell types in which this phenomenon occurs. The ultimate significance of transactivation-dependent signalling remains to be defined but it appears to be prominent and if so will represent a new cell signalling frontier.  相似文献   
12.
Reconsideration on Homogeneous Quadratic Riemann Boundary Value Problem   总被引:1,自引:0,他引:1  
The homogeneous quadratic Riemann boundary value problem (1) with Hoelder continuous coefficients for the normal case was considered by the author in 1997. But the solutions obtained there are incomplete. Here its general method of solution is obtained.  相似文献   
13.
Abrupt climate change:Debate or action   总被引:4,自引:1,他引:3  
Global abrupt climate changes have been documented by various climate records, including ice cores, ocean sediment cores, lake sediment cores, cave deposits, loess deposits and pollen records. The climate system prefers to be in one of two stable states, i.e. interstadial or stadial conditions, but not in between. The transition between two states has an abrupt character. Abrupt climate changes are, in general, synchronous in the northern hemisphere and tropical regions. The timescale for abrupt climate changes can be as short as a decade. As the impacts may be potentially serious, we need to take actions such as reducing CO2 emissions to the atmosphere.  相似文献   
14.
We prove that the model with physical and human capital adjustment costs has optimal solution when the production function is increasing return and the structure of vetor fields of the model changes substantially when the prodution function from decreasing return turns to increasing return. And it is shown that the economy is improved when the coefficients of adjustment costs become small.  相似文献   
15.
B S Qiu  C H Cho  C W Ogle 《Experientia》1992,48(4):389-391
Ten-day treatment with nicotine (5, 25 or 50 micrograms/ml drinking water) dose-dependently intensified gastric ulceration induced by cold-restraint, and emptying rate. Stomach contractions produced by graded doses of bethanechol i.v. were elevated further by nicotine treatment. It is suggested that chronic nicotine administration produces hypersensitivity of the gastric muscarinic receptors; stomach hypermotility contributes to the ulcer-worsening action of the alkaloid.  相似文献   
16.
复数,实数及实对称数据下Bruun FFT算法的实现   总被引:3,自引:0,他引:3  
本文在复数、实数以及实对称数据下研究和实现了Bruun FFT算法。文章分析和评价了各种数据下BruunFFT的运算量和特点,提出了算法的实现结构和方法。最后给了TMS320C30上的运算时间,我们实现的算法比基2FFT速度提高35%。  相似文献   
17.
18.
19.
20.
The method of extracting and describing the intended behavior of software precisely has become one of the key points in the fields of software behavior's dynamic and trusted authentication. In this paper, the author proposes a specified measure of extracting SIBDS (software intended behaviors describing sets) statically from the binary executable using the software's API functions invoking, and also introduces the definition of the structure used to store the SIBDS in detail. Experimental results demonstrate that the extracting method and the storage structure definition offers three strong properties: (i) it can describe the software's intended behavior accurately; (ii) it demands a small storage expense; (iii) it provides strong capability to defend against mimicry attack.  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