全文获取类型
收费全文 | 25647篇 |
免费 | 82篇 |
国内免费 | 102篇 |
专业分类
系统科学 | 128篇 |
丛书文集 | 136篇 |
教育与普及 | 48篇 |
理论与方法论 | 85篇 |
现状及发展 | 10564篇 |
研究方法 | 1114篇 |
综合类 | 13336篇 |
自然研究 | 420篇 |
出版年
2013年 | 215篇 |
2012年 | 386篇 |
2011年 | 774篇 |
2010年 | 161篇 |
2008年 | 417篇 |
2007年 | 528篇 |
2006年 | 515篇 |
2005年 | 482篇 |
2004年 | 453篇 |
2003年 | 438篇 |
2002年 | 480篇 |
2001年 | 974篇 |
2000年 | 949篇 |
1999年 | 559篇 |
1992年 | 526篇 |
1991年 | 419篇 |
1990年 | 462篇 |
1989年 | 470篇 |
1988年 | 438篇 |
1987年 | 446篇 |
1986年 | 436篇 |
1985年 | 512篇 |
1984年 | 462篇 |
1983年 | 383篇 |
1982年 | 358篇 |
1981年 | 342篇 |
1980年 | 360篇 |
1979年 | 840篇 |
1978年 | 682篇 |
1977年 | 577篇 |
1976年 | 549篇 |
1975年 | 560篇 |
1974年 | 726篇 |
1973年 | 555篇 |
1972年 | 594篇 |
1971年 | 752篇 |
1970年 | 920篇 |
1969年 | 644篇 |
1968年 | 717篇 |
1967年 | 623篇 |
1966年 | 602篇 |
1965年 | 422篇 |
1964年 | 130篇 |
1959年 | 210篇 |
1958年 | 380篇 |
1957年 | 252篇 |
1956年 | 197篇 |
1955年 | 186篇 |
1954年 | 182篇 |
1948年 | 150篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
31.
Summary The nature of antigen Dd, an antigen present in the extracts of human dandruff which precipitates human sera selectively, and antibodies reacting with it are reported.This work was supported through U.G.C. Grant No. F.23-230/75/SR II. H.K. participated in this study, first as J.R.F. of U.G.C. and then as S.R.F. of I.C.M.R. We are grateful to Dr Baruch S. Blumberg for his invaluable suggestions and to Professor H. Walter for the gift of IgG, IgM and IgA immune sera. 相似文献
32.
当 Kjell Ekhorn 还在学校学习图形设计,Jon Forss 已在这个行业里工作了不少年头。1989年 Jon Forss 于1LeicesterPolytechnic 毕业后就在 Bath 为一家广告代理商工作,四年之后他移居伦敦为 namara 设计公司设计图书封面。五年以后,他遇到从伦敦 Centrl St.Martins 学校毕业不过两年,正以自由职业者身份从事图书封面设计、图片制作和摄影工作的 Kjell Ekhorn。两人惊讶于互相对图书封面设计的看法,一时相见恨晚,然后自然而然的开始了两人合作的NON-FORMAT 时代。 相似文献
33.
34.
A topoisomerase II inhibitor, novobiocin, and a deacetylase inhibitor, butyrate, synergistically transformed human liver cells into fibroblast-like cells. This morphological change was associated with an increased production of procollagen type III peptide and a simultaneous assembly of actin, tubulin, vimentin and cytokeratin. Novobiocin and butyrate had no marked effect on the phosphorylation state of cytokeratin proteins, but synergistically enhanced [3H]acetate uptake. From these results, it can be speculated that protein acetylation plays an important role in inducing the assembly of cytoskeletal proteins and the morphological transformation of human liver cells. 相似文献
35.
Aspirin-like drugs may block pain independently of prostaglandin synthesis inhibition 总被引:2,自引:0,他引:2
K. Brune W. S. Beck G. Geisslinger S. Menzel-Soglowek B. M. Peskar B. A. Peskar 《Cellular and molecular life sciences : CMLS》1991,47(3):257-261
Summary Using flurbiprofen, a chiral anti-inflammatory and analgesic 2-arylpropionic acid derivative, the enantiomers of which are not converted to each other (less than 5%) in rats or man, we obtained evidence that prostaglandin synthesis inhibition is primarily mediating the anti-inflammatory activity but prostaglandin synthesis independent mechanisms contribute to the analgesic effects. Thus, the S-form inhibited prostaglandin synthesis, inflammation and nociception in rats. The R-form had much less effect on prostaglandin synthesis and did not affect inflammation. It did, however, block nociception in rats almost as potently as the S-form. S-flurbiprofen, in contrast to the R-form, was clearly ulcerogenic in the gastrointestinal mucosa. These results indicate additional molecular mechanisms of analgesia and suggest the use of R-arylpropionic acids as analgesics. 相似文献
36.
The genetic engineering of production traits in domestic animals 总被引:1,自引:0,他引:1
37.
We develop in this paper an efficient way to select the best subset threshold autoregressive model. The proposed method uses a stochastic search idea. Differing from most conventional approaches, our method does not require us to fix the delay or the threshold parameters in advance. By adopting the Markov chain Monte Carlo techniques, we can identify the best subset model from a very large of number of possible models, and at the same time estimate the unknown parameters. A simulation experiment shows that the method is very effective. In its application to the US unemployment rate, the stochastic search method successfully selects lag one as the time delay and five best models from more than 4000 choices. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
38.
M E MacDonald A Novelletto C Lin D Tagle G Barnes G Bates S Taylor B Allitto M Altherr R Myers 《Nature genetics》1992,1(2):99-103
Analysis of 78 Huntington's disease (HD) chromosomes with multi-allele markers revealed 26 different haplotypes, suggesting a variety of independent HD mutations. The most frequent haplotype, accounting for about one third of disease chromosomes, suggests that the disease gene is between D4S182 and D4S180. However, the paucity of an expected class of chromosomes that can be related to this major haplotype by assuming single crossovers may reflect the operation of other mechanisms in creating haplotype diversity. Some of these mechanisms sustain alternative scenarios that do not require a multiple mutational origin for HD and/or its positioning between D4S182 and D4S180. 相似文献
39.
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