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   34669篇
  免费   61篇
  国内免费   85篇
系统科学   162篇
丛书文集   726篇
教育与普及   81篇
理论与方法论   202篇
现状及发展   15150篇
研究方法   1444篇
综合类   16658篇
自然研究   392篇
  2013年   219篇
  2012年   466篇
  2011年   893篇
  2010年   199篇
  2008年   600篇
  2007年   598篇
  2006年   645篇
  2005年   655篇
  2004年   595篇
  2003年   614篇
  2002年   617篇
  2001年   1072篇
  2000年   965篇
  1999年   660篇
  1992年   631篇
  1991年   508篇
  1990年   535篇
  1989年   527篇
  1988年   525篇
  1987年   549篇
  1986年   526篇
  1985年   661篇
  1984年   548篇
  1983年   453篇
  1982年   380篇
  1981年   377篇
  1980年   499篇
  1979年   1094篇
  1978年   952篇
  1977年   915篇
  1976年   667篇
  1975年   723篇
  1974年   1037篇
  1973年   872篇
  1972年   902篇
  1971年   1129篇
  1970年   1477篇
  1969年   1111篇
  1968年   1051篇
  1967年   1085篇
  1966年   928篇
  1965年   685篇
  1964年   180篇
  1959年   394篇
  1958年   581篇
  1957年   478篇
  1956年   397篇
  1955年   339篇
  1954年   391篇
  1948年   214篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
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   
62.
P Villa  J Courtin 《Nature》1991,351(6328):613-614
  相似文献   
63.
P Meyrand  J Simmers  M Moulins 《Nature》1991,351(6321):60-63
  相似文献   
64.
T lymphocytes recognize antigen in the form of peptides that associate with specific alleles of class I or class II major histocompatibility (MHC) molecules. By contrast with the clear MHC allele-specific binding of peptides to purified class II molecules purified solubilized class I molecules either bind relatively poorly or show degenerate specificity. Using photo-affinity labelling, we demonstrate here the specific interaction of peptides with cell-associated MHC class I molecules and show that this involves metabolically active processes.  相似文献   
65.
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   
66.
J M Nunnari  D L Zimmerman  S C Ogg  P Walter 《Nature》1991,352(6336):638-640
The rough endoplasmic reticulum membranes of mammalian cells contain specific ribosome-binding sites. A purification to apparent homogeneity of a negatively charged protein (ERp180) of relative molecular mass 180,000 (180 K) was reported which was proposed to function as a rough endoplasmic reticulum ribosome receptor. We report here that ribosome-binding site activity quantitatively solubilized from rough endoplasmic reticulum membranes does not cofractionate with ERp180. By contrast, ribosome-binding site activity fractionates as a much smaller, positively charged protein.  相似文献   
67.
BARNOTHY J 《Nature》1948,161(4096):681
  相似文献   
68.
69.
    
Summary If amphibian gastrulæ are heated at 36 to 37°C for one hour, their development is blocked irreversibly; if, however, the dorsal lip is removed from these blocked gastrulæ and implanted in a normal gastrula, its development is resumed and the host is the site of a neural induction.  相似文献   
70.
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