全文获取类型
收费全文 | 1829篇 |
免费 | 127篇 |
专业分类
1956篇 |
出版年
2023年 | 15篇 |
2022年 | 28篇 |
2021年 | 41篇 |
2020年 | 28篇 |
2019年 | 41篇 |
2018年 | 47篇 |
2017年 | 31篇 |
2016年 | 56篇 |
2015年 | 71篇 |
2014年 | 84篇 |
2013年 | 128篇 |
2012年 | 131篇 |
2011年 | 115篇 |
2010年 | 74篇 |
2009年 | 76篇 |
2008年 | 90篇 |
2007年 | 89篇 |
2006年 | 94篇 |
2005年 | 82篇 |
2004年 | 66篇 |
2003年 | 72篇 |
2002年 | 58篇 |
2001年 | 47篇 |
2000年 | 44篇 |
1999年 | 29篇 |
1998年 | 7篇 |
1997年 | 10篇 |
1996年 | 10篇 |
1995年 | 11篇 |
1994年 | 12篇 |
1992年 | 19篇 |
1991年 | 14篇 |
1990年 | 22篇 |
1989年 | 31篇 |
1988年 | 9篇 |
1987年 | 15篇 |
1986年 | 13篇 |
1985年 | 11篇 |
1984年 | 7篇 |
1983年 | 12篇 |
1982年 | 9篇 |
1981年 | 11篇 |
1979年 | 11篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1976年 | 12篇 |
1975年 | 11篇 |
1970年 | 6篇 |
1968年 | 8篇 |
1966年 | 5篇 |
排序方式: 共有1956条查询结果,搜索用时 15 毫秒
21.
Arun Agrawal 《Human ecology: an interdisciplinary journal》1993,21(3):261-279
This paper describes and then analyzes the decision-making arrangements that prevail among the Raikas—nomadic shepherds from Western India. The paper suggests, using a simple analytical framework, that the existing distribution of decision-making during migration helps the Raikasto utilize available economies of scale, represent the different interest groups in their collectives, and control their decision-makers. At the same time, the ordinary shepherds in the camp are able to extract a comfortable subsistence from a complex and harsh environment by delegating much of their decision-making responsibilities to the leaders in the camp. To the extent shepherds in other parts of the world migrate over long distances and must confront similar issues of delegation of responsibilities and control over decision-makers, the analysis holds general relevance. 相似文献
22.
23.
Enzymatic labeling of nucleic acids is a fundamental tool in molecular biology with virtually every aspect of nucleic acid
hybridization technique involving the use of labeled probes. Different methods for enzymatic labeling of DNA, RNA and oligonucleotide
probes are available today. In this review, we will describe both radioactive and nonradioactive labeling methods, yet the
choice of system for labeling the probe depends on the application under study. 相似文献
24.
25.
Sublocalization of an Ataxia-Telangiectasia Gene Distal to D11S384 by Ancestral Haplotyping In Costa Rican Families 总被引:8,自引:4,他引:4 下载免费PDF全文
Nancy Uhrhammer Ethan Lange Oscar Porras Arash Naeim Xiaoguang Chen Sepideh Sheikhavandi Sujata Chiplunkar Lan Yang Sugandha Dandekar Teresa Liang Nima Patel Sharon Teraoka Nitin Udar Nidia Calvo Patrick Concannon Kenneth Lange Richard A. Gatti 《American journal of human genetics》1995,57(1):103-111
In an effort to localize a gene for ataxia-telangiectasia (A-T), we have genotyped 27 affected Costa Rican families, with 13 markers, in the chromosome 11q22-23 region. Significant linkage disequilibrium was detected for 9/13 markers between D11S1816 and D11S1391. Recombination events observed in these pedigrees places A-T between D11S1819 and D11S1960. One ancestral haplotype is common to 24/54 affected chromosomes and roughly two-thirds of the families. Inferred (ancestral) recombination events involving this common haplotype in earlier generations suggest that A-T is distal to D11S384 and proximal to D11S1960. Several other common haplotypes were identified, consistent with multiple mutations in a single gene. When considered together with all other evidence, this study further sublocalizes the major A-T locus to ≈200 kb, between markers S384 and S535. 相似文献
26.
Myelin was found to contain five major glycoproteins with molecular weights of 120000, 95000, 88000, 43000 and 38000. Light myelin contained only 5-7% of the amount of these glycoproteins in whole myelin, whereas heavy myelin and the membrane fraction contained amounts nearly identical with whole myelin. Since all the major and minor glycoproteins, with the exception of 120000-mol-wt. glycoprotein, were detected only after treating the myelin membrane with neuraminidase, N-acetylneuraminic acid is a terminal sugar residue in these glycoproteins. 相似文献
27.
Enzymatic studies have been performed on a local strain of Aspergillus niger to find a correlation with citric acid accumulation. The activity of aconitase [aconitate hydratase, citrate(isocitrate) hydrolyase, EC 4.2.1.3] and isocitrate dehydrogenase (NADP+) [threo-ds-isocitrate:NADP+ oxidoreductase (decarboxylating) EC 1.1.1.42] decreased after 4 days whereas that of citrate synthase [citrate oxaloacetate-lyase (pro-3S-CH2COO?→acetylCoA), EC 4.1.3.7] did so after 8 days, when citric acid accumulation in the medium reached a maximum (45.9 mg ml?1). In vitro studies with mycelial cell-free extracts demonstrated inhibition of citrate synthase activity by sodium azide and potassium ferricyanide on both the 4th and 8th days. Aconitase was inhibited by sodium arsenate, sodium fluoride, iodoacetic acid and potassium ferricyanide only on the 4th day. Isocitrate dehydrogenase (NADP+) activity on the 4th and 8th days was inhibited by iodoacetic acid but was stimulated by potassium ferricyanide. The possible existence of isozyme species of these enzymes is discussed. 相似文献
28.
NMR spectroscopy in the structural elucidation of oligosaccharides and glycosides. 总被引:28,自引:0,他引:28
P K Agrawal 《Phytochemistry》1992,31(10):3307-3330
The potential of one- and two-dimensional NMR techniques for the identification of individual sugar residues, their anomeric configuration, interglycosidic linkages, sequencing and the site of any appended group, in establishing the structures of naturally occurring oligosaccharides and glycosides is presented. 相似文献
29.
Examination of 15-day-old rabbit brain myelin proteins by sodium dodecyl sulfate-slab gel electrophoresis revealed the presence of a basic protein with a molecular weight of 21,000 (21K protein) which was not previously reported in this species. This protein exhibited characteristic bluish green color with amido black and gave an amino acid composition strikingly similar to large basic protein (LBP). It formed a line of identity with LBP when diffused against antiserum to chicken brain basic protein. The concentration of LBP (18.9 micrograms/mg of dry myelin) is 6-fold greater than that of the 21K protein(3.31 micrograms/mg of dry myelin) in rabbit brain myelin. After the intracerebral injection of [32P]orthophosphoric acid, both LBP and 21K protein were found to be phosphorylated. [32P]Phosphate in the purified preparations of these proteins was covalently linked by phosphoester bonds to serine and threonine residues. The specific radioactivity of the 21K protein (84,693 cpm/mg of protein) was not significantly higher than LBP (69,797 cpm/mg of protein). 相似文献
30.