全文获取类型
收费全文 | 31213篇 |
免费 | 85篇 |
国内免费 | 117篇 |
专业分类
系统科学 | 137篇 |
丛书文集 | 379篇 |
教育与普及 | 72篇 |
理论与方法论 | 103篇 |
现状及发展 | 14312篇 |
研究方法 | 1261篇 |
综合类 | 14806篇 |
自然研究 | 345篇 |
出版年
2013年 | 203篇 |
2012年 | 400篇 |
2011年 | 741篇 |
2008年 | 514篇 |
2007年 | 562篇 |
2006年 | 583篇 |
2005年 | 570篇 |
2004年 | 631篇 |
2003年 | 542篇 |
2002年 | 505篇 |
2001年 | 975篇 |
2000年 | 940篇 |
1999年 | 611篇 |
1994年 | 371篇 |
1992年 | 580篇 |
1991年 | 432篇 |
1990年 | 495篇 |
1989年 | 465篇 |
1988年 | 413篇 |
1987年 | 482篇 |
1986年 | 515篇 |
1985年 | 646篇 |
1984年 | 471篇 |
1983年 | 436篇 |
1982年 | 411篇 |
1981年 | 401篇 |
1980年 | 409篇 |
1979年 | 1053篇 |
1978年 | 834篇 |
1977年 | 764篇 |
1976年 | 630篇 |
1975年 | 695篇 |
1974年 | 916篇 |
1973年 | 790篇 |
1972年 | 770篇 |
1971年 | 901篇 |
1970年 | 1174篇 |
1969年 | 905篇 |
1968年 | 914篇 |
1967年 | 886篇 |
1966年 | 762篇 |
1965年 | 608篇 |
1964年 | 194篇 |
1959年 | 319篇 |
1958年 | 541篇 |
1957年 | 387篇 |
1956年 | 321篇 |
1955年 | 317篇 |
1954年 | 309篇 |
1948年 | 235篇 |
排序方式: 共有10000条查询结果,搜索用时 653 毫秒
221.
W. D. MacRae G. F. Q. Chan Chi-Kit Wat G. H. N. Towers J. Lam 《Cellular and molecular life sciences : CMLS》1980,36(9):1096-1097
Summary -Terthienyl and 5 polyacetylenes were examined for chromosome damaging activity using Syrian hamster cells. None of these naturally occurring compounds induced sister chromatid exchanges and neither -terthienyl nor phenylheptatriyne induced chromosome aberrations.The authors wish to thank the National Science and Engineering Research Council for financial support of this research. 相似文献
222.
Summary Prostaglandins (PGs) E2, F2, and I2 were examined for their effects on the electrical and mechanical activities of isolated rat, rabbit and guinea-pig hearts. All PGs produced dysrhythmias in rat hearts at low concentrations only, while higher concentrations were antiarrhythmic. Guinea-pig hearts were less responsive while rabbit hearts were completely resistant.We thank the Manitoba Heart Foundation for financial support and Dr J. Pike (Upjohn, Kalamazoo, MI, USA) for gifts of prostaglandins. Dr M. Karmazyn is a Fellow of the Canadian Heart Foundation. 相似文献
223.
Summary Direct incorporation and cold trap experiments suggest that cholest-4-en-3-one is an intermediate in the conversion of cholesterol into 3-hydroxymethyl-A-nor-cholestane in the marine spongeAxinella verrucosa. Cholest-4-en-3-one is further transformed by the sponge into cholest-4-en-3-ol, 5-cholestan-3-one and 5-cholestan-3-ol; these compounds arise from side reactions, which are not part of the major metabolic route leading to 3-hydroxymethyl-A-norsteranes. 相似文献
224.
Summary After a dose of 3.0 Gy in the peak position of the pion depth-dose curve, the ratios between observed chromosome aberration yields under conditions of oxygenation and of anoxia were obtained for lymphocytes exposed at 3 depths in a plastic phantom. These ratios were 3.7, 1.9 and 1.3 in the plateau, peak and post-peak positions, respectively, suggesting a corresponding decrease in the oxygen enhancement ratio.Acknowledgments. We wish to thank Dr D.H. Reading, Mr M.A. Hynes and Mr W. Spinks for their assistance at the Rutherford Laboratory's -II beam line. This work was partly supported by Euratom Contract 171-76-1 BIO-UK. 相似文献
225.
C. R. Pace-Asciak N. S. Edwards M. C. Carrara 《Cellular and molecular life sciences : CMLS》1980,36(6):635-637
Summary Tritium-labelled PGF2 was administered i.v. into rats of varying ages (2, 4, 6 weeks and adult). Urine was collected and assayed for radioactive products by thin-layer-chromatography. Results showed a distinctly different urinary profile between the 2-week-old and the adult rat. While the urinary pattern from the 2-week-old rat gave a single less polar product than PGF2, the pattern from the adult rat gave products more polar than PGF2. Urine from the 4- and 6-week-old rats gave a mixture of these types of products. These results indicate that some prostaglandin catabolic pathway (likely the -oxidative system) is activated in vivo within the 4–6-week postnatal period in the rat.Supported by a grant (MT-4181) to C.P.-A. from the Medical Research Council of Canada.This study is in partial fulfillment of the requirements for a Ph.D. degree in the Department of Pharmacology, University of Toronto. 相似文献
226.
Summary 2-Halogeno-ethanols change the active site structure of -chymotrypsin more rapidly and effectively than ethanol, 1-propanol and urea, probably before producing an extensive conformation change. 相似文献
227.
G. B. Glavin 《Cellular and molecular life sciences : CMLS》1980,36(1):79-80
Summary Rats given aluminium hydroxide after cold-restraint stress but before the post-stress delay period, ulcerated significantly less severely and less frequently than rats given the drug before cold-restraint stress or those given water at either time period. Both aluminium hydroxide treated groups exhibited less ulceration than non-drug groups. These data suggest profound parasympathetic and hence, gastric acid, involvement in restraint delay-induced ulceration in rats. 相似文献
228.
229.
E. Knecht J. Renau-Piqueras J. Hernández-Yago S. Grisolía 《Cellular and molecular life sciences : CMLS》1981,37(5):456-457
Summary Protein from resting or phytohemagglutinin-stimulated human peripheral blood T-lymphocytes, pulse-labeled in vitro for 1 h with3H-leucine, had a half-life of 30 h. 相似文献
230.
T. Kuroiwa S. Nishibayashi S. Kawano T. Suzuki 《Cellular and molecular life sciences : CMLS》1981,37(9):969-971
Summary DNA-containing areas in various phages (T4, , T7 and 29) could be observed at the light microscopic level using ethidium bromide epi-fluorescent microscopy. The fluorescent intensity per phage was in linear proportion to the DNA content in each phage.Acknowledgements. This work was supported in part by the grant No. 521708 and No. 511212 from the Japan Ministry of Education, Science and Culture. 相似文献