全文获取类型
收费全文 | 29143篇 |
免费 | 143篇 |
国内免费 | 214篇 |
专业分类
系统科学 | 183篇 |
丛书文集 | 484篇 |
教育与普及 | 43篇 |
理论与方法论 | 111篇 |
现状及发展 | 12341篇 |
研究方法 | 1279篇 |
综合类 | 14584篇 |
自然研究 | 475篇 |
出版年
2013年 | 250篇 |
2012年 | 454篇 |
2011年 | 929篇 |
2010年 | 204篇 |
2008年 | 518篇 |
2007年 | 634篇 |
2006年 | 572篇 |
2005年 | 613篇 |
2004年 | 685篇 |
2003年 | 652篇 |
2002年 | 823篇 |
2001年 | 1052篇 |
2000年 | 944篇 |
1999年 | 661篇 |
1992年 | 568篇 |
1991年 | 396篇 |
1990年 | 424篇 |
1989年 | 412篇 |
1988年 | 412篇 |
1987年 | 420篇 |
1986年 | 459篇 |
1985年 | 588篇 |
1984年 | 410篇 |
1983年 | 337篇 |
1982年 | 298篇 |
1981年 | 324篇 |
1980年 | 375篇 |
1979年 | 879篇 |
1978年 | 690篇 |
1977年 | 668篇 |
1976年 | 536篇 |
1975年 | 523篇 |
1974年 | 782篇 |
1973年 | 645篇 |
1972年 | 717篇 |
1971年 | 775篇 |
1970年 | 1094篇 |
1969年 | 855篇 |
1968年 | 730篇 |
1967年 | 759篇 |
1966年 | 721篇 |
1965年 | 534篇 |
1964年 | 185篇 |
1959年 | 268篇 |
1958年 | 525篇 |
1957年 | 365篇 |
1956年 | 283篇 |
1955年 | 255篇 |
1954年 | 297篇 |
1948年 | 186篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
261.
262.
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
263.
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
264.
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
265.
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
266.
V. R. Osório E Castro M. G. P. Vale A. P. Carvalho 《Cellular and molecular life sciences : CMLS》1976,32(4):424-426
Summary The effect of the antibiotic X-537A on the phosphorylated ATPase (EP) was investigated. The results show that X-537A depresses the level of EP which is dependent on the Ca2+ gradient, while the Ca2+-independent EP is not affected.
Acknowledgments. This work was supported by grants from the Instituto de Alta Cultura of the Portuguese Ministry of Education (No. CB/2) and the Calouste Gulbenkian Foundation. 相似文献
267.
G. M. Hanozet M. Simonetta D. Barisio A. Guerritore 《Cellular and molecular life sciences : CMLS》1976,32(10):1246-1249
Summary The three enzymes of ethanol metabolism alcohol dehydrogenase, aldehyde dehydrogenase and acetyl-CoA synthetase in the obligate aerobic yeastRhodotorula gracilis are repressed by glucose and induced by C2 metabolic fuels with a regulatory pattern indicating a correlation in the control mechanisms. To try an identification of the molecular signals involved in the transmission of the inducing stimulus, experiments were carried out by blocking with 2 mM pyrazole the ethanol acetaldehyde metabolic step. Results indicate that ethanol is not specifically required as a molecular signal for induction.This work was supported by a grant from the Italian Consiglio Nazionale delle Ricerche. 相似文献
268.
Summary The central and the peripheral areas of the head-fold stage rat embryo ectoderm develop into both the neural tissue and the epidermis when grafted under the kidney capsule of adult rats.This investigation was supported by the grant No. IV/3 from the Research Foundation of S.R. Croatia, and in part by NIH PL 480 Agreement No. 02-038-1. 相似文献
269.
Summary Tryptic treatment of muscle thick filaments reveals the underlying backbones of aggregatedl-meromyosin as a coli of 3 secondary filaments (helical repeat 130 nm) each in turn a coli of a 3 finer ones. 相似文献
270.
A. J. Rein D. D. Saperstein S. H. Pines P. C. Radlick 《Cellular and molecular life sciences : CMLS》1976,32(10):1352-1354
Summary Using Raman spectroscopy, we demonstrate that low levels of -carotene, lycopene, and xanthophyll give rise to resonance enhanced bands in blood plasma. These results explain the significance of previously unidentified spectral maxima which have been related to the state of health of the blood donor. 相似文献