全文获取类型
收费全文 | 23992篇 |
免费 | 289篇 |
国内免费 | 410篇 |
专业分类
系统科学 | 407篇 |
丛书文集 | 340篇 |
教育与普及 | 276篇 |
理论与方法论 | 92篇 |
现状及发展 | 5826篇 |
研究方法 | 789篇 |
综合类 | 16642篇 |
自然研究 | 319篇 |
出版年
2015年 | 220篇 |
2014年 | 263篇 |
2013年 | 388篇 |
2012年 | 457篇 |
2011年 | 823篇 |
2010年 | 324篇 |
2009年 | 331篇 |
2008年 | 609篇 |
2007年 | 665篇 |
2006年 | 610篇 |
2005年 | 546篇 |
2004年 | 533篇 |
2003年 | 596篇 |
2002年 | 742篇 |
2001年 | 1137篇 |
2000年 | 997篇 |
1999年 | 818篇 |
1998年 | 379篇 |
1997年 | 380篇 |
1996年 | 360篇 |
1995年 | 310篇 |
1994年 | 306篇 |
1993年 | 281篇 |
1992年 | 527篇 |
1991年 | 453篇 |
1990年 | 456篇 |
1989年 | 454篇 |
1988年 | 419篇 |
1987年 | 346篇 |
1986年 | 326篇 |
1985年 | 325篇 |
1984年 | 274篇 |
1983年 | 248篇 |
1980年 | 212篇 |
1979年 | 502篇 |
1978年 | 391篇 |
1977年 | 365篇 |
1976年 | 302篇 |
1975年 | 348篇 |
1974年 | 497篇 |
1973年 | 377篇 |
1972年 | 386篇 |
1971年 | 491篇 |
1970年 | 607篇 |
1969年 | 413篇 |
1968年 | 448篇 |
1967年 | 377篇 |
1966年 | 384篇 |
1965年 | 259篇 |
1958年 | 225篇 |
排序方式: 共有10000条查询结果,搜索用时 305 毫秒
71.
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
72.
73.
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
74.
Genotoxic effects of dithane M-45 were studied on the bone marrow cells of male albino mice (Lacca strain) in vivo. Different doses (30 mg, 40 mg and 300 mg/kg b.wt) of dithane M-45 were injected intraperitoneally and their effects were investigated after time intervals of 1, 2, 5 and 10 days. The chromosomal aberrations observed in the bone marrow cells of male mice after treatment with dithane M-45 were fragments, rings, dicentric chromosomes, terminal chromatid deletions, chromatid gaps and breaks. In addition to these chromosomal aberrations, physiological effects such as uneven stretching of chromatin material, end-to-end chromosomal associations, exchange configurations, clumping, stickiness and centromeric associations were also observed. 相似文献
75.
76.
基于Windows NT的HRPS-Ⅱ设备的控制系统设计 总被引:1,自引:0,他引:1
介绍了华中科技大学开发的HRPS-Ⅱ型选择性激光烧结设备的体系结构,根据选择性激光烧结的工作原理并结合该系统的硬件结构开发了基于NT操作系统下的控制软件.该控制软件是一种分层的结构,各个不同优先级的任务在不同的层面上运行,实时性强的部分运行在硬件中断级别上,对控制软件的关键性技术进行了描述.通过试验运行,该设备成功地加工出了复杂的原型件,证明控制系统开发是成功的. 相似文献
77.
78.
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
79.
80.