全文获取类型
收费全文 | 24255篇 |
免费 | 44篇 |
国内免费 | 79篇 |
专业分类
系统科学 | 100篇 |
丛书文集 | 368篇 |
教育与普及 | 70篇 |
理论与方法论 | 117篇 |
现状及发展 | 10652篇 |
研究方法 | 1073篇 |
综合类 | 11600篇 |
自然研究 | 398篇 |
出版年
2013年 | 179篇 |
2012年 | 378篇 |
2011年 | 773篇 |
2010年 | 161篇 |
2008年 | 463篇 |
2007年 | 465篇 |
2006年 | 481篇 |
2005年 | 496篇 |
2004年 | 464篇 |
2003年 | 425篇 |
2002年 | 423篇 |
2001年 | 655篇 |
2000年 | 645篇 |
1999年 | 441篇 |
1992年 | 403篇 |
1991年 | 315篇 |
1990年 | 344篇 |
1989年 | 343篇 |
1988年 | 349篇 |
1987年 | 340篇 |
1986年 | 341篇 |
1985年 | 470篇 |
1984年 | 346篇 |
1983年 | 269篇 |
1982年 | 242篇 |
1981年 | 252篇 |
1980年 | 304篇 |
1979年 | 726篇 |
1978年 | 553篇 |
1977年 | 568篇 |
1976年 | 484篇 |
1975年 | 504篇 |
1974年 | 687篇 |
1973年 | 598篇 |
1972年 | 643篇 |
1971年 | 704篇 |
1970年 | 908篇 |
1969年 | 769篇 |
1968年 | 778篇 |
1967年 | 703篇 |
1966年 | 643篇 |
1965年 | 479篇 |
1964年 | 148篇 |
1959年 | 268篇 |
1958年 | 483篇 |
1957年 | 353篇 |
1956年 | 325篇 |
1955年 | 268篇 |
1954年 | 295篇 |
1948年 | 234篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
161.
E. Viggiani 《Cellular and molecular life sciences : CMLS》1979,35(9):1265-1266
Summary A method able to monitor transmitted light acoustically is described. It makes use of an amplifier of light variations, provided with a photocell and a sound device, a photometer, an optic probe and a special support.Acknowledgments. The author would like to thank Dr Leonard Salzarulo, chairman of the Physics Department of the New Jersey Institute of Technology, for the critical reading of the paper. The author acknowledges the invaluable assistance of Prof. Araldo Ramundo of the Centro Regionale Professionale in Cosenza, Italy, for designing and assembling the electronic amplifier. Appreciation is also extended to Prof. Giuseppe Battendieri of the Liceo Scientifico Enrico Fermi in Cosenza, Italy, for the schematic reproduction of the apparatus. 相似文献
162.
E. Ch. Herrmann 《Cellular and molecular life sciences : CMLS》1979,35(9):1263-1264
Summary The simple theoretical criterion for chemical carcinogenicity based on the average quasi-valence number is discussed and shown to be inappropriate as a reliable indicator of carcinogenicity of any organic compound.I thank very much Dr R. Gordon for reading the English text and also for a stimulating discussion. 相似文献
163.
F. Caviezel M. Poli A. M. Girardi G. Pozza 《Cellular and molecular life sciences : CMLS》1979,35(10):1402-1404
Summary The insulinemic response to 1 g of tolbutamide i.v. is greatly enhanced (+145%) after a 60-min infusion of the -lytic dihydrogenated ergot alkaloid, dihydroergocristine (83.3 m/min, corresponding to a total dose of 5 mg) in 7 healthy subjects. No differences are observed in the glycemic responses.Acknowledgment. The authors are grateful to Mr Franco Della Sala, M.D., for his skillful technical assistance. 相似文献
164.
MEASUREMENT of the absolute value of absorption by water vapour at microwave frequencies is difficult because the effect is so small. Far in the wings of the absorption lines, in the so-called 'windows' of the spectrum, it is especially difficult to achieve high accuracy in the free atmosphere. But it is in these windows that the behaviour of the absorption is important from both applied and scientific points of view. Satellite communications, remote sensing of the atmosphere, and radioastronomy, are all influenced by this behaviour. Measurements on an Earth-space path are reported here; the results indicate a nonlinear relationship between absorption and water-vapour content. 相似文献
165.
0957 + 561 A, B are two QSOs of mag 17 with 5.7 arc s separation at redshift 1.405. Their spectra leave little doubt that they are associated. Difficulties arise in describing them as two distinct objects and the possibility that they are two images of the same object formed by a gravitational lens is discussed. 相似文献
166.
167.
168.
IT has been suggested that the bacterial flora of the rumen should be considered as three distinct, interacting populations-the bacteria of rumen fluid (the population which has been studied most extensively), the bacteria associated with food particles, and the bacteria adhering to the epithelial wall of the organ(1). Until now, studies of the 'epithelial' population have been restricted to examination of postmortem samples of wall tissue and its attached bacterial flora(2-5). A recently developed technique(6) for feeding young sheep for long periods solely by infusion of protein and other essential nutrients into the abomasum, and of volatile fatty acids and bicarbonate buffer into the rumen, has provided us with an opportunity to study in isolation the role of the bacterial population of the wall in the ecomicrobiology of the rumen in the living animal. Our studies show that this population can exist independently of the other two populations, that it is primarily responsible for urea digestion in the rumen and that it initiates breakdown of dead epithelial tissue. Furthermore, our results point to an inverse relationship between ammonia concentration and ureolytic activity in rumen fluid, which may account for the control which ammonia exerts over flux of urea across the rumen wall(7-9). 相似文献
169.
170.