全文获取类型
收费全文 | 26292篇 |
免费 | 53篇 |
国内免费 | 78篇 |
专业分类
系统科学 | 98篇 |
丛书文集 | 333篇 |
教育与普及 | 56篇 |
理论与方法论 | 105篇 |
现状及发展 | 12267篇 |
研究方法 | 1047篇 |
综合类 | 12218篇 |
自然研究 | 299篇 |
出版年
2013年 | 156篇 |
2012年 | 338篇 |
2011年 | 630篇 |
2010年 | 143篇 |
2008年 | 369篇 |
2007年 | 425篇 |
2006年 | 426篇 |
2005年 | 436篇 |
2004年 | 535篇 |
2003年 | 422篇 |
2002年 | 398篇 |
2001年 | 740篇 |
2000年 | 689篇 |
1999年 | 510篇 |
1992年 | 455篇 |
1991年 | 359篇 |
1990年 | 408篇 |
1989年 | 391篇 |
1988年 | 370篇 |
1987年 | 392篇 |
1986年 | 404篇 |
1985年 | 523篇 |
1984年 | 364篇 |
1983年 | 349篇 |
1982年 | 336篇 |
1981年 | 322篇 |
1980年 | 364篇 |
1979年 | 877篇 |
1978年 | 695篇 |
1977年 | 682篇 |
1976年 | 548篇 |
1975年 | 639篇 |
1974年 | 810篇 |
1973年 | 701篇 |
1972年 | 750篇 |
1971年 | 835篇 |
1970年 | 1056篇 |
1969年 | 839篇 |
1968年 | 854篇 |
1967年 | 840篇 |
1966年 | 695篇 |
1965年 | 545篇 |
1964年 | 165篇 |
1959年 | 278篇 |
1958年 | 511篇 |
1957年 | 362篇 |
1956年 | 294篇 |
1955年 | 278篇 |
1954年 | 253篇 |
1948年 | 200篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
91.
92.
Genetic variation of supernatant and mitochondrial malate dehydrogenase isozymes in the teleost Fundulus heteroclitus 总被引:3,自引:0,他引:3
G S Whitt 《Experientia》1970,26(7):734-736
93.
94.
Genetics of the alkaline phosphatase polymorphism of the human placenta 总被引:27,自引:0,他引:27
95.
G. Deby-Dupont J. Pincemail A. Thirion C. Deby M. Lamy P. Franchimont 《Cellular and molecular life sciences : CMLS》1991,47(9):952-957
In order to obtain a radioimmunoassay (RIA) technique for the measurement of human plasma myeloperoxidase (MPO), we purified the enzyme from polymorphonuclear granulocytes (neutrophils), and compared three methods of labeling it with125Iodine: chloramine T, lactoperoxidase, and an original technique of self labeling based on the ability of the enzyme to oxidize and bind125I in the presence of H2O2. The chloramine T technique produced a degraded protein, as well shown by a high non-specific binding of tracer to antibody. The lactoperoxidase technique did not succeed in labeling MPO with an adequate specific activity. In contrast, the self-labeling method gave a stable tracer with a specific activity of 23 Ci/gmg MPO (85 MBq), a satisfactory level of immunoreactivity, and a low-specific binding (3%). After labeling, purification of tracer was achieved by gel filtration chromatography in phosphate buffer (0.05 M; pH7) to which 0.1% poly-L-lysine was added. The labeled molecule remained stable for 40 days and could be used for RIA with a polyclonal antibody raised in rabbits. 相似文献
96.
J. L. Lacuara S. R. de Barioglio P. P. de Oliva A. S. Bernacchi A. F. de Culasso J. A. Castro B. M. Franke de Cazzulo J. J. Cazzulo 《Cellular and molecular life sciences : CMLS》1991,47(6):612-616
Summary The tricyclic anti-calmodulin drug trifluoperazine (TFP) inhibited growth and motility of epimastigotes ofTrypanosoma cruzi, at concentrations lower than 100 M, and motility and infectivity of the bloodstream trypomastigote form at 200 M. Electron microscopy of TFP-treated epimastigotes showed that the major effect was at the mitochondrial level, with gross swelling and disorganization. The oligomycin-sensitive, mitochondrial ATPase was completely inhibited by 20 M TFP, and the same drug concentration caused a 60% decrease in intracellular ATP content. The results suggest that the trypanocidal effect of TFP may be related more to mitochondrial damage than to the well-known anticalmodulin effect of the drug. 相似文献
97.
The endangered Kemp's ridley sea turtle (Lepidochelys kempi) nests almost exclusively at a single locality in the western Gulf of Mexico, whereas the olive ridley (L. olivacea) nests globally in warm oceans. Morphological similarities between kempi and olivacea, and a geographical distribution that "...makes no sense at all under modern conditions of climate and geography", raise questions about the degree of evolutionary divergence between these taxa. Analysis of mitochondrial (mt) DNA restriction sites shows that Kemp's ridley is distinct from the olive ridley in matriarchal phylogeny, and that the two are sister taxa with respect to other marine turtles. Separation of olive and the Kemp's ridley lineages may date to formation of the Isthmus of Panama, whereas the global spread of the olive ridley lineage occurred recently. In contrast to recent examples in which molecular genetic assessments challenged systematic assignments underlying conservation programmes, our mtDNA data corroborate the taxonomy of an endangered form. 相似文献
98.
A. A. Stierle R. Upadhyay J. Hershenhorn G. A. Strobel G. Molina 《Cellular and molecular life sciences : CMLS》1991,47(8):853-859
Black Sigatoka is the most costly to control disease of bananas and plantains in the world. Currently, a worldwide search is underway either to find or to produce cultivars that are disease-resistant or-tolerant. Phytotoxins isolated from the pathogen might facilitate the discovery of such cultivars. Several aromatic compounds from liquid cultures ofMycosphaerella fijiensis, the causal agent of Black Sigatoka disease of bananas and plantains, have been isolated. The most abundant and phytotoxic of these compounds is 2,4,8-trihydroxytetralone, which induces necrotic lesions at 5 g/5 l in less than 12 h on sensitive cultivars of bananas. This compound exhibits host-selectivity that mimics that of the pathogen. Other phytotoxins isolated from this fungus, in lesser amounts, were juglone, the novel compound 2-carboxy-3-hydroxycinnamic acid, isoochracinic acid and 4-hydroxyscytalone. Some of the phytotoxins isolated are melanin shunt pathway metabolites, which makes this fungus unique among plant pathogens. 相似文献
99.
100.
Summary The in vitro absorption of calcium from the duodenum was significantly less in a group of rats fed on a wheat diet than in a group fed a wheat and Bengal gram (7030) diet. 相似文献