全文获取类型
收费全文 | 17664篇 |
免费 | 41篇 |
国内免费 | 77篇 |
专业分类
系统科学 | 66篇 |
丛书文集 | 173篇 |
教育与普及 | 67篇 |
理论与方法论 | 54篇 |
现状及发展 | 7869篇 |
研究方法 | 723篇 |
综合类 | 8621篇 |
自然研究 | 209篇 |
出版年
2012年 | 217篇 |
2011年 | 409篇 |
2009年 | 100篇 |
2008年 | 288篇 |
2007年 | 315篇 |
2006年 | 293篇 |
2005年 | 313篇 |
2004年 | 352篇 |
2003年 | 314篇 |
2002年 | 310篇 |
2001年 | 481篇 |
2000年 | 523篇 |
1999年 | 344篇 |
1994年 | 306篇 |
1992年 | 282篇 |
1991年 | 233篇 |
1990年 | 292篇 |
1989年 | 266篇 |
1988年 | 271篇 |
1987年 | 293篇 |
1986年 | 308篇 |
1985年 | 348篇 |
1984年 | 241篇 |
1983年 | 266篇 |
1982年 | 217篇 |
1981年 | 212篇 |
1980年 | 255篇 |
1979年 | 522篇 |
1978年 | 450篇 |
1977年 | 410篇 |
1976年 | 328篇 |
1975年 | 400篇 |
1974年 | 496篇 |
1973年 | 434篇 |
1972年 | 449篇 |
1971年 | 587篇 |
1970年 | 641篇 |
1969年 | 542篇 |
1968年 | 554篇 |
1967年 | 477篇 |
1966年 | 422篇 |
1965年 | 303篇 |
1964年 | 132篇 |
1959年 | 166篇 |
1958年 | 323篇 |
1957年 | 253篇 |
1956年 | 203篇 |
1955年 | 200篇 |
1954年 | 194篇 |
1948年 | 167篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
881.
D. A. S. Smith 《Cellular and molecular life sciences : CMLS》1978,34(7):845-846
Summary
Danaus chrysippus grows faster and attains significantly greater size when fed as a larva on several species of Asclepiadaceae (milkweeds) containing cardiac glycosides than on one which does not.Acknowledgment. I thank Professor D. Schneider and Dr M. Boppré for sending me a sample of butterflies of Kenya stock reared in the Federal Republic of Germany. 相似文献
882.
883.
Summary Phenylhydrazine produces in the red blood cell the same effect as the enzymic system xanthine oxidase-xanthine, a superoxide radical generator system. Both effects are inhibited by the enzyme superoxide dismutase.This work was supported in part by grants Nos. 1045 and 3243 of Oficina Técnica de Desarrollo Científico y Creación Artística de la Universidad de Chile. 相似文献
884.
H Garcin P Higueret 《Comptes rendus des séances de l'Académie des sciences. Série D, Sciences naturelles》1977,285(5):531-533
During the 9 post-weaning weeks there is not in the vitamin A-deficient Rats the regular decrease of the thyroxinemia which occurs in the control Rats. So the vitamin A-deficient Rats studied in plateau of weight have a total thyroxinemia greater than that of control Rats (+71%). It is possible to speculate that numerous symptoms of the deficiency are the result of this hyperthyroxinemia. 相似文献
885.
H D Picton 《Nature》1978,274(5674):888-889
886.
887.
Summary Complexes of pyridine-2-carbothioamide with diethyltin dichloride, dibenzyltin dichloride and phenyltin trichloride are described. In each case, the chelating agent is bound to the tin(IV) atom by the pyridine nitrogen and the carbothioamide sulphur, giving support to proposals that certain organotin compounds cause enzyme deactivation via the formation of tin-sulphur bonds.Acknowledgment. We thank the Tin Industry (Research and Development) Board, Kuala Lumpur, for financial support. 相似文献
888.
Single crystals of oxycobalt-myoglobin were examined by electron paramagnetic resonance (EPR) spectroscopy at ambient and cryogenic temperatures. The principal values and eigenvectors of the g-tensor and the hyperfine coupling tensor were determined. The Co--O--O bond angle was estimated to be 125 degrees at ambient temperature. The single crystal EPR dats of oxycobalt myoglobin at 77K showed two sets of the principal values for g and hyperfine coupling tensors and eigenvectors, indication that the bound oxygen molecule takes two distinct orientations. The result has demonstrated for the first time that the well defined change in the molecular orientation is induced upon freezing the biological macromolecule. 相似文献
889.
890.
Summary The involvement of the noradrenergic system in hypothermia induced by intrahypothalamically-injected carbachol (CCh) was studied by depleting hypothalamic noradrenaline (NA) with the catecholamine neurotoxin 6-hydroxydopamine (6-OHDA) and repeating the CCh injections after 6-OHDA treatment. The results suggest that noradrenergic neurons may be involved in hypothermia produced by CCh in the pigeon. 相似文献