全文获取类型
收费全文 | 26020篇 |
免费 | 61篇 |
国内免费 | 63篇 |
专业分类
系统科学 | 139篇 |
丛书文集 | 289篇 |
教育与普及 | 64篇 |
理论与方法论 | 140篇 |
现状及发展 | 11690篇 |
研究方法 | 1016篇 |
综合类 | 12395篇 |
自然研究 | 411篇 |
出版年
2013年 | 151篇 |
2012年 | 314篇 |
2011年 | 777篇 |
2010年 | 130篇 |
2008年 | 368篇 |
2007年 | 411篇 |
2006年 | 463篇 |
2005年 | 454篇 |
2004年 | 562篇 |
2003年 | 445篇 |
2002年 | 428篇 |
2001年 | 688篇 |
2000年 | 676篇 |
1999年 | 476篇 |
1992年 | 444篇 |
1991年 | 347篇 |
1990年 | 379篇 |
1989年 | 377篇 |
1988年 | 350篇 |
1987年 | 389篇 |
1986年 | 413篇 |
1985年 | 533篇 |
1984年 | 378篇 |
1983年 | 336篇 |
1982年 | 300篇 |
1981年 | 315篇 |
1980年 | 326篇 |
1979年 | 823篇 |
1978年 | 668篇 |
1977年 | 633篇 |
1976年 | 521篇 |
1975年 | 587篇 |
1974年 | 814篇 |
1973年 | 678篇 |
1972年 | 674篇 |
1971年 | 832篇 |
1970年 | 1084篇 |
1969年 | 799篇 |
1968年 | 793篇 |
1967年 | 800篇 |
1966年 | 734篇 |
1965年 | 550篇 |
1964年 | 210篇 |
1959年 | 286篇 |
1958年 | 504篇 |
1957年 | 349篇 |
1956年 | 305篇 |
1955年 | 286篇 |
1954年 | 266篇 |
1948年 | 226篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
181.
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
182.
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
183.
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
184.
185.
Y. Kakiuchi G. M. Hughes T. Arai M. Horimoto Y. Kikuchi T. Koyama 《Cellular and molecular life sciences : CMLS》1981,37(4):376-377
Summary A needle type of colloid osmometer has been devised with special attachments which made it useable with 3-l samples. It has been used in oncometry of fresh water teleosts to give the following results: 5.1±1.0 mm Hg for goldfish, 5.2±0.71 mm Hg for carp, and 14.3±0.75 mm Hg for eel.This study was supported in part by Research Grant 387036 from the Ministry of Education of Japan.invited to National Institute of Physiological Sciences, Okazaki, Japan. 相似文献
186.
187.
188.
Summary Autoradiographic, stereological and histological studies have been carried out to determine the origin of muscle fibre splitting which supposedly occurs during muscle hypertrophy. The results obtained clearly indicate that the supposedly split fibres are a transient response probably derived from satellite cells and are not derived from pre-existing fibres by true splitting. Similarly, increases in muscle fibre size are not achieved by recruitment of satellite structures as indicated by lack of myonuclear recruitment.Acknowledgment. This work was carried out with the aid of a grant from the Medical Research Council of Great Britain. The authors are grateful for the excellent technical assistance of Miss H. Caulton, M.J. Wild and M. Fenner. 相似文献
189.
Summary Thymidylate synthetase (methylenetetrahydrofolate: 2-deoxyuridine-5-monophosphate C-methyltransferase; EC 2.1.1.45) from neonatal mouse liver has been purified 714-fold by affinity chromatography on aminohexylsepharose bound 10-methyl-5,8-dideazafolate.Supported by grant CA22754, awarded by the National Cancer Institute, DHEW. 相似文献
190.
G. Cimino A. Crispino S. De Rosa S. De Stefano G. Sodano 《Cellular and molecular life sciences : CMLS》1981,37(9):924-926
Summary Several high molecular weight polyacetylenes have been isolated from the spongePetrosia ficiformis found in dark caves. These compounds are related to, but different from, the polyacetylenes isolated from the same sponge living in its usual habitat.This work is a part of the Progetto finalizzato per l'Oceanografia e i Fondi Marini, CNR, Roma.The authors thank Mr G. Scognamiglio for the HPLC work, Mr C. Di Pinto for the NMR spectra and Mr G. Villani for the collection of the sponge. 相似文献