全文获取类型
收费全文 | 22755篇 |
免费 | 63篇 |
国内免费 | 55篇 |
专业分类
系统科学 | 235篇 |
丛书文集 | 493篇 |
教育与普及 | 46篇 |
理论与方法论 | 65篇 |
现状及发展 | 9555篇 |
研究方法 | 939篇 |
综合类 | 11151篇 |
自然研究 | 389篇 |
出版年
2013年 | 138篇 |
2012年 | 295篇 |
2011年 | 701篇 |
2010年 | 108篇 |
2008年 | 353篇 |
2007年 | 395篇 |
2006年 | 424篇 |
2005年 | 409篇 |
2004年 | 400篇 |
2003年 | 399篇 |
2002年 | 331篇 |
2001年 | 712篇 |
2000年 | 718篇 |
1999年 | 420篇 |
1992年 | 410篇 |
1991年 | 364篇 |
1990年 | 387篇 |
1989年 | 326篇 |
1988年 | 368篇 |
1987年 | 366篇 |
1986年 | 342篇 |
1985年 | 484篇 |
1984年 | 363篇 |
1983年 | 303篇 |
1982年 | 239篇 |
1981年 | 256篇 |
1980年 | 346篇 |
1979年 | 689篇 |
1978年 | 581篇 |
1977年 | 551篇 |
1976年 | 472篇 |
1975年 | 531篇 |
1974年 | 663篇 |
1973年 | 579篇 |
1972年 | 588篇 |
1971年 | 701篇 |
1970年 | 925篇 |
1969年 | 726篇 |
1968年 | 624篇 |
1967年 | 653篇 |
1966年 | 596篇 |
1965年 | 433篇 |
1964年 | 113篇 |
1959年 | 265篇 |
1958年 | 400篇 |
1957年 | 303篇 |
1956年 | 269篇 |
1955年 | 238篇 |
1954年 | 263篇 |
1948年 | 176篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
152.
153.
154.
Summary After injection of microspheres into both renal arteries of rats, an irreversible shock syndrome develops, resulting in death within 4–12 h. Ligation of both renal pedicles after injection of microspheres prevents the shock. It is presumed that kininogenases released from the kidneys participate in the pathogenesis of the shock syndrome.These studies were supported in part by the Deutsche Forschungsgemeinschaft within the SFB 90, Cardiovasculäres System. 相似文献
155.
Summary The present results show that the sensitivity of the chick myocardium to the positive motropic effect of Ca++ decreases during development and that the Ca++ concentration of the physiological solution used must be lowered below normal to study the effects of positive inotropic agents in preparations from younger embryos. Isoproterenol elicits positive inotropic responses in 7–9-day embryonic ventricle and in newborn chick atria; however, the 4-day embryonic myocardium is unresponsive to isoproterenol.This work was supported by Grant No. HL-15995 from the National Heart Institute (USPHS).The authors would like to thank Dr.F. E. Shideman for the isolated tissue baths used in these experiments. 相似文献
156.
A. R. Jones Carole Murcott D. H. Milton Jennifer Flynn 《Cellular and molecular life sciences : CMLS》1977,33(7):934-935
Summary The male antifertility agent 1-amino-3-chloropropan-2-ol (ACP,I) has been shown to be metabolized to-chlorohydrin (III) and metabolites of-chlorohydrin. This accounts for the similar antifertility and renal toxicity effects of both compounds. 相似文献
157.
M. D. Adams J. T. Earnhardt B. R. Martin L. S. Harris W. L. Dewey R. K. Razdan 《Cellular and molecular life sciences : CMLS》1977,33(9):1204-1205
Summary Abnormal-8-tetrahydrocannabidiol (ABN-8-THC) failed to elicit central nervous system and cardiovascular effects in laboratory animals. Abnormal-cannabidiol (ABN-CBD) was also devoid of overt behavioral effects but produced marked hypotension with only slight bradycardia in anesthesized dogs.Acknowledgment. This work was supported by NIDA (grant No. DA-00574-01 and DA-00490) and Virginia Heart Society (grant No. RR-05697) 相似文献
158.
R. K. Raina D. Njoroge J. N. Ng'ang'a B. V. Telang 《Cellular and molecular life sciences : CMLS》1977,33(11):1499-1500
Summary
Naja mossambica pallida venom administered i.v. (300 /kg) produces an initial brief fall in blood pressure, due to a direct myocardial depressant effect, and a sustained fall due to central depressant effect.This study was supported by University of Nairobi research grants (670–376). We also thank Mr E. Njogu for photographic assistance. 相似文献
159.
S. Y. Dike Meera Kamath J. R. Merchant 《Cellular and molecular life sciences : CMLS》1977,33(8):985-985
Summary A one-step synthesis of hexahydrocannabinoid analogs (HHC) is described making use of the condensation of phenolic ketones and aldehydes with citronellal in the presence of pyridine.Grateful thanks are accorded to Drs L. Chopard and S. Selvavinayakam for spectral measurements and Dr I. Fleming for useful discussion.R. Mechoulam and Y. Gaoni, Recent advances in the chemistry of Hashish, in: Progress in the Chemistry of Organic natural products, vol. 25, p. 175. Ed. L. Zechmeister. Springer Verlag, Wien 1967; R. Mechoulam, Marijuana Chemistry and Pharmacology, metabolism and clinical effects. Academic Press, New York 1973; R. Mechoulam, N. K. McCallum and S. Burstein, Chem. Rev.76, 75 (1976). 相似文献
160.
L. Minale C. Pizza R. Riccio F. Zollo 《Cellular and molecular life sciences : CMLS》1983,39(6):569-571
Summary On the basis of comparative spectral data, the structures of 3 novel steroidal glycosides from the Mediterranean starfishHacelia attenuata have been elucidated as3, 4 and5. These are further examples of a novel group of 24-O-glycosidated steroids recently encountered in the same species and in the Pacific speciesProtoreaster nodosus.Part 9. L. Minale, C. Pizza, R. Riccio and F. Zollo, Experientia39 (1983) 567. This contribution is part of the Progetto Finalizzato Chimica fine e secondaria del C.N.R., Roma.Acknowledgments. We thank Prof. K. Nakanishi, Columbia University, New York, for FD-mass spectral analyses, the Centro Interfacoltà di Metodologie Chimico-Fisiche for 270 MHz NMR facilities, and Miss R. Aquino for part of the experimental work. 相似文献