全文获取类型
收费全文 | 36555篇 |
免费 | 128篇 |
国内免费 | 121篇 |
专业分类
系统科学 | 190篇 |
丛书文集 | 792篇 |
教育与普及 | 90篇 |
理论与方法论 | 214篇 |
现状及发展 | 16030篇 |
研究方法 | 1500篇 |
综合类 | 17554篇 |
自然研究 | 434篇 |
出版年
2013年 | 210篇 |
2012年 | 477篇 |
2011年 | 962篇 |
2010年 | 217篇 |
2009年 | 180篇 |
2008年 | 636篇 |
2007年 | 649篇 |
2006年 | 675篇 |
2005年 | 672篇 |
2004年 | 706篇 |
2003年 | 646篇 |
2002年 | 646篇 |
2001年 | 1116篇 |
2000年 | 1040篇 |
1999年 | 719篇 |
1992年 | 637篇 |
1991年 | 537篇 |
1990年 | 551篇 |
1989年 | 552篇 |
1988年 | 550篇 |
1987年 | 569篇 |
1986年 | 571篇 |
1985年 | 701篇 |
1984年 | 571篇 |
1983年 | 461篇 |
1982年 | 404篇 |
1981年 | 435篇 |
1980年 | 529篇 |
1979年 | 1134篇 |
1978年 | 998篇 |
1977年 | 974篇 |
1976年 | 672篇 |
1975年 | 758篇 |
1974年 | 1074篇 |
1973年 | 911篇 |
1972年 | 950篇 |
1971年 | 1155篇 |
1970年 | 1523篇 |
1969年 | 1158篇 |
1968年 | 1086篇 |
1967年 | 1147篇 |
1966年 | 965篇 |
1965年 | 727篇 |
1959年 | 400篇 |
1958年 | 601篇 |
1957年 | 504篇 |
1956年 | 423篇 |
1955年 | 358篇 |
1954年 | 424篇 |
1948年 | 232篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
62.
M. Ishibashi M. Tsuda Y. Ohizumi T. Sasaki J. Kobayashi 《Cellular and molecular life sciences : CMLS》1991,47(3):299-300
Summary A new bromotyrosine-derived alkaloid with antileukemic activity, purealidin A (5), has been isolated from the Okinawan marine spongePsammaplysilla purea and its chemical structure elucidated on the basis of the spectroscopic data. 相似文献
63.
Aeromonas caviae isolated from stools of diarrheic formula-fed infants and environmental sources produce acetic acid when grown in glucose broth, which is bactericidal (suicide phenomenon). A. caviae grows anaerobically in a minimal medium or under permissive conditions such as the intestinal tract of formula-fed infants. These isolates adhered to HEp-2 cells and produced a cytotoxic and a cytotonic enterotoxin which underscore their enteropathogenicity. 相似文献
64.
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
65.
66.
67.
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
68.
Structure of the detoxification catalyst mercuric ion reductase from Bacillus sp. strain RC607 总被引:10,自引:0,他引:10
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
69.
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
70.