全文获取类型
收费全文 | 68762篇 |
免费 | 295篇 |
国内免费 | 566篇 |
专业分类
系统科学 | 1256篇 |
丛书文集 | 586篇 |
教育与普及 | 288篇 |
理论与方法论 | 537篇 |
现状及发展 | 35575篇 |
研究方法 | 1492篇 |
综合类 | 27698篇 |
自然研究 | 2191篇 |
出版年
2013年 | 819篇 |
2012年 | 807篇 |
2011年 | 2938篇 |
2009年 | 630篇 |
2008年 | 1019篇 |
2007年 | 1230篇 |
2006年 | 1226篇 |
2005年 | 1449篇 |
2004年 | 2624篇 |
2003年 | 2169篇 |
2002年 | 1869篇 |
2001年 | 1860篇 |
2000年 | 1367篇 |
1999年 | 1246篇 |
1998年 | 649篇 |
1997年 | 778篇 |
1994年 | 699篇 |
1993年 | 695篇 |
1992年 | 1201篇 |
1991年 | 974篇 |
1990年 | 1074篇 |
1989年 | 880篇 |
1988年 | 866篇 |
1987年 | 870篇 |
1986年 | 915篇 |
1985年 | 1124篇 |
1984年 | 919篇 |
1983年 | 813篇 |
1982年 | 883篇 |
1981年 | 911篇 |
1980年 | 1018篇 |
1979年 | 1784篇 |
1978年 | 1540篇 |
1977年 | 1537篇 |
1976年 | 1306篇 |
1975年 | 1313篇 |
1974年 | 1378篇 |
1973年 | 1499篇 |
1972年 | 1609篇 |
1971年 | 1702篇 |
1970年 | 1994篇 |
1969年 | 1711篇 |
1968年 | 1618篇 |
1967年 | 1528篇 |
1966年 | 1336篇 |
1965年 | 1041篇 |
1959年 | 581篇 |
1958年 | 915篇 |
1957年 | 700篇 |
1956年 | 577篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
721.
722.
Unique Golgi apparatus and vesicle formation in a red alga. 总被引:2,自引:0,他引:2
723.
724.
We examined effects of several vasoactive peptides (substance P, physalaemin, neurotensin, bradykinin, angiotensin etc.) on the excitability of molluscan giant neurones identified in the subesophageal ganglia of Achatina fulica Férussac. Of these peptides, only physalaemin showed a remarkable excitatory effect on a giant tonically autoactive neurone. 相似文献
725.
The crude petroleum ether, chloroform and alcoholic extracts from the roots of Aristolochia indica (Linn.) showed 100% interceptive activity in mature female mice at the single dose of 100 mg/kg body wt. The follow-up studies with the chloroform extract showed the most significant effect in the basic part and two acidic fractions at the single dose levels of 50 mg/kg body wt. No toxic effect was observed at the dose levels used. 相似文献
726.
Summary The C-11 proton of an aprophine possessing a C-1,2 methylenedioxy group falls relatively upfield between 7.47 and 7.86. Additionally, the i.c.s. for the two protons of the methylenedioxy group is large (4–12 Hz). The presence of a methylenedioxy at C-3,4 in a phenanthrene alkaloid also results in an upfield shift ( 8.95–9.00) of the C-5 proton.This project was supported by NIH research grant No. HL-12971, awarded by the National Heart and Lung Institute, PHS/DHEW. 相似文献
727.
Summary The effect of dipyridamole on platelet phospholipids has been studied. After the platelet incubation with dipyridamole, a 38% reduction in the concentration of the sphingomyelin and a 21% increase in phosphatidyl choline were produced. 相似文献
728.
Ca2+-stimulated ATPase activity of sarcoplasmic reticulum (SR) preparations is activated after a short period of preincubation at temperatures between 40 and 45 degrees C, but for temperatures higher than 48 degrees C pronounced denaturation is observed. Heat denaturation is decreased if Mg2+ or K+ are present during heat treatment. 相似文献
729.
The hyperthermic effect of a bacterial pyrogen has been studied in rabbits pretreated or not with p-chlorophenylalanine or 5, 6-dihydroxytryptamine. The results obtained indicate that a selective reduction of cerebral 5-hydroxytryptamine levels by these drugs do not significantly affect pyrogen hypertermia. 相似文献
730.
A A Hakim 《Experientia》1976,32(8):1057-1059
Trypsin-like protease with wide spectrum of enzymatic activities have been isolated from cell-free medium from in vivo cultured human mammary carcinoma cells, and from peripheral blood lymphocytes of patients with mammary carcinoma cultured in presence of cell-membrane carcinoma-associated glycoprotein. 相似文献