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   36775篇
  免费   642篇
  国内免费   70篇
系统科学   1202篇
丛书文集   717篇
教育与普及   80篇
理论与方法论   458篇
现状及发展   14286篇
研究方法   1370篇
综合类   19002篇
自然研究   372篇
  2018年   765篇
  2017年   772篇
  2016年   508篇
  2012年   692篇
  2011年   1781篇
  2010年   983篇
  2009年   580篇
  2008年   1059篇
  2007年   1296篇
  2006年   615篇
  2005年   638篇
  2004年   646篇
  2003年   726篇
  2002年   628篇
  2001年   978篇
  2000年   897篇
  1999年   598篇
  1992年   570篇
  1991年   466篇
  1990年   486篇
  1989年   489篇
  1988年   490篇
  1987年   498篇
  1986年   490篇
  1985年   599篇
  1984年   494篇
  1983年   405篇
  1982年   346篇
  1981年   341篇
  1980年   448篇
  1979年   968篇
  1978年   855篇
  1977年   846篇
  1976年   581篇
  1975年   630篇
  1974年   931篇
  1973年   785篇
  1972年   804篇
  1971年   1017篇
  1970年   1342篇
  1969年   1004篇
  1968年   946篇
  1967年   989篇
  1966年   829篇
  1965年   609篇
  1959年   360篇
  1958年   522篇
  1957年   443篇
  1956年   366篇
  1954年   363篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
This article presents a case example involving the renaming of an organizational change process from BPR to outsourcing. The paper discusses the important ramifications of such a name change in that the recognition of outsourcing allowed an organizational commitment to counseling and termination advice. The paper discusses two ways of looking at the name change, one from a critical theory perspective and one from a realist perspective. It demonstrates how theory can provide useful yet markedly different interpretations of such organizational events. Critical theory operates from within what can be termed the transitive epistemological dimension, whereas critical realism tends to emphasize the importance of ontological issues. Each has important things to say about the situation and improves our understanding overall.  相似文献   
52.
P Villa  J Courtin 《Nature》1991,351(6328):613-614
  相似文献   
53.
P Meyrand  J Simmers  M Moulins 《Nature》1991,351(6321):60-63
  相似文献   
54.
Several hundred million tons of toxic mercurials are dispersed in the biosphere. Microbes can detoxify organo-mercurials and mercury salts through sequential action of two enzymes, organomercury lyase and mercuric ion reductase (MerA). The latter, a homodimer with homology to the FAD-dependent disulphide oxidoreductases, catalyses the reaction NADPH + Hg(II)----NADP+ + H+ + Hg(0), one of the very rare enzymic reactions with metal substrates. Human glutathione reductase serves as a reference molecule for FAD-dependent disulphide reductases and between its primary structure and that of MerA from Tn501 (Pseudomonas), Tn21 (Shigella), p1258 (Staphylococcus) and Bacillus, 25-30% of the residues have been conserved. All MerAs have a C-terminal extension about 15 residues long but have very varied N termini. Although the enzyme from Streptomyces lividans has no addition, from Pseudomonas aeruginosa Tn501 and Bacillus sp. strain RC607 it has one and two copies respectively of a domain of 80-85 residues, highly homologous to MerP, the periplasmic component of proteins encoded by the mer operon. These domains can be proteolytically cleaved off without changing the catalytic efficiency. We report here the crystal structure of MerA from the Gram-positive bacterium Bacillus sp. strain RC607. Analysis of its complexes with nicotinamide dinucleotide substrates and the inhibitor Cd(II) reveals how limited structural changes enable an enzyme to accept as substrate what used to be a dangerous inhibitor. Knowledge of the mode of mercury ligation is a prerequisite for understanding this unique detoxification mechanism.  相似文献   
55.
BARNOTHY J 《Nature》1948,161(4096):681
  相似文献   
56.
57.
58.
We consider the stability of a random Riccati equation with a Markovian binary jump coefficient. More specifically, we are concerned with the boundedness of the solution of a random Riccati difference equation arising from Kalman filtering with measurement losses. A sufficient condition for the peak covariance stability is obtained which has a simpler form and is shown to be less conservative in some cases than a very recent result in existing literature. Furthermore, we show that a known sufficient condition is also necessary when the observability index equals one.  相似文献   
59.
In the present paper, we focus on constructive spherical codes. By employing algebraic geometry codes, we give an explicit construction of spherical code sequences. By making use of the idea involved in the proof of the Gilbert-Varshamov bound in coding theory, we construct a spherical code sequence in exponential time which meets the best-known asymptotic bound by Shamsiev and Wyner.  相似文献   
60.
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