全文获取类型
收费全文 | 30286篇 |
免费 | 202篇 |
国内免费 | 233篇 |
专业分类
系统科学 | 418篇 |
丛书文集 | 643篇 |
教育与普及 | 99篇 |
理论与方法论 | 84篇 |
现状及发展 | 12250篇 |
研究方法 | 1097篇 |
综合类 | 15684篇 |
自然研究 | 446篇 |
出版年
2013年 | 284篇 |
2012年 | 489篇 |
2011年 | 957篇 |
2010年 | 290篇 |
2009年 | 252篇 |
2008年 | 560篇 |
2007年 | 622篇 |
2006年 | 611篇 |
2005年 | 560篇 |
2004年 | 636篇 |
2003年 | 523篇 |
2002年 | 454篇 |
2001年 | 938篇 |
2000年 | 934篇 |
1999年 | 587篇 |
1992年 | 504篇 |
1991年 | 462篇 |
1990年 | 474篇 |
1989年 | 414篇 |
1988年 | 444篇 |
1987年 | 446篇 |
1986年 | 432篇 |
1985年 | 589篇 |
1984年 | 452篇 |
1983年 | 362篇 |
1982年 | 308篇 |
1981年 | 347篇 |
1980年 | 430篇 |
1979年 | 907篇 |
1978年 | 732篇 |
1977年 | 693篇 |
1976年 | 573篇 |
1975年 | 644篇 |
1974年 | 816篇 |
1973年 | 706篇 |
1972年 | 745篇 |
1971年 | 865篇 |
1970年 | 1139篇 |
1969年 | 887篇 |
1968年 | 778篇 |
1967年 | 837篇 |
1966年 | 740篇 |
1965年 | 548篇 |
1959年 | 305篇 |
1958年 | 484篇 |
1957年 | 370篇 |
1956年 | 332篇 |
1955年 | 280篇 |
1954年 | 330篇 |
1948年 | 221篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
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
52.
LANE RE 《Advancement of science》1948,5(18):96-118
53.
54.
55.
56.
R. Auerbach 《Cellular and molecular life sciences : CMLS》1948,4(12):473-474
Summary The preceding empirical relation was found between the surface tension of liquids, the specific weight of liquids, and the velocity of sound:=6.3 · 10–4
3/2. In place of the vèocity of sound can be used, with suitable changes in the equation, the compressibility or, in the case of solid substances, the elasticity of the material in question. The range of validity of this relation is so large that it is possible by means of it to calculate the surface tension of solid substances and of gases. 相似文献
57.
1 Results In addition to single wall and multiwall carbon nanotubes[1], several structures,which are more or less related to fullerenes,including carbon nanohorns[2a], carbon nanospheres[2b] and onion like carbon structures[2c] have been reported.A new simple straight forward method to access some of these structures is the solid-state pyrolysis of different organometallic complexes in a sealed vessel,which led so far to carbon nanotubes[3a,b], carbon nanocables[3c] and onions[3d]. 相似文献
58.
59.
60.