全文获取类型
收费全文 | 21158篇 |
免费 | 80篇 |
国内免费 | 64篇 |
专业分类
系统科学 | 174篇 |
丛书文集 | 289篇 |
教育与普及 | 38篇 |
理论与方法论 | 79篇 |
现状及发展 | 10135篇 |
研究方法 | 878篇 |
综合类 | 9505篇 |
自然研究 | 204篇 |
出版年
2013年 | 136篇 |
2012年 | 301篇 |
2011年 | 520篇 |
2010年 | 158篇 |
2008年 | 333篇 |
2007年 | 357篇 |
2006年 | 397篇 |
2005年 | 396篇 |
2004年 | 481篇 |
2003年 | 358篇 |
2002年 | 344篇 |
2001年 | 583篇 |
2000年 | 551篇 |
1999年 | 388篇 |
1992年 | 372篇 |
1991年 | 277篇 |
1990年 | 290篇 |
1989年 | 284篇 |
1988年 | 248篇 |
1987年 | 272篇 |
1986年 | 320篇 |
1985年 | 391篇 |
1984年 | 300篇 |
1983年 | 265篇 |
1982年 | 249篇 |
1981年 | 249篇 |
1980年 | 272篇 |
1979年 | 680篇 |
1978年 | 551篇 |
1977年 | 532篇 |
1976年 | 409篇 |
1975年 | 469篇 |
1974年 | 682篇 |
1973年 | 552篇 |
1972年 | 582篇 |
1971年 | 657篇 |
1970年 | 833篇 |
1969年 | 651篇 |
1968年 | 662篇 |
1967年 | 653篇 |
1966年 | 543篇 |
1965年 | 456篇 |
1964年 | 167篇 |
1959年 | 218篇 |
1958年 | 378篇 |
1957年 | 291篇 |
1956年 | 234篇 |
1955年 | 224篇 |
1954年 | 224篇 |
1948年 | 164篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
X-linked gene for testicular feminization in the mouse 总被引:38,自引:0,他引:38
92.
Somatic translocation of antibody genes 总被引:36,自引:0,他引:36
93.
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
94.
Descending pathways with monosynaptic action on motoneurones 总被引:2,自引:0,他引:2
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.
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
97.
98.
99.
Because of possible variation in venom composition, an understanding of venomous snake systematics is of great importance for the optimization of antivenom treatment of snakebite patients. Intraspecific variation in the morphology of many venomous snakes complicates the definition and indentification of some species when allopatric populations are involved. Selectively neutral or near-neutral mtDNA sequences can reveal evolutionary relationships obscured by ecogenetically-caused morphological variation. We use comparative sequencing of the cytochrome oxidase subunit 1 gene to reveal the existence of a widespread, cryptic species of spiting cobra from southeast Asia. This species,Naja siamensis, is widely sympatric with other Asiatic cobra species. This may be of considerable medical significance, and calls for further research into venom composition in Asiatic cobras. 相似文献
100.
C. Baroni Urbani G. S. Boyan A. Blarer J. Billen T. M. Musthak Ali 《Cellular and molecular life sciences : CMLS》1994,50(1):63-71
The Indian antHarpegnathos saltator may be unique among insects in using its jumping capacity not only as an escape mechanism but also as a normal means of locomotion, and for catching its prey in flight. High-speed cinematography used to analyse the various phases of the jump suggests thatHarpegnathos employs a novel jumping mechanism to mediate these behaviours: namely the synchronous activation of its middle and hindlegs. Electrophysiological recordings from muscles or nerves in pairs of middle and hindlegs show remarkably synchronous activity during fictive jumping, supporting the synchronous activation hypothesis.Harpegnathos is not the only ant to jump, and a cladistic analysis suggests that jumping behaviour evolved independently three times during ant evolutionary history. 相似文献