全文获取类型
收费全文 | 232787篇 |
免费 | 2250篇 |
国内免费 | 801篇 |
专业分类
化学 | 116841篇 |
晶体学 | 3996篇 |
力学 | 10760篇 |
综合类 | 1篇 |
数学 | 25508篇 |
物理学 | 78732篇 |
出版年
2020年 | 1787篇 |
2019年 | 2043篇 |
2018年 | 2721篇 |
2017年 | 2652篇 |
2016年 | 3914篇 |
2015年 | 2390篇 |
2014年 | 3967篇 |
2013年 | 10074篇 |
2012年 | 7532篇 |
2011年 | 9396篇 |
2010年 | 6686篇 |
2009年 | 6629篇 |
2008年 | 8704篇 |
2007年 | 8737篇 |
2006年 | 8272篇 |
2005年 | 7493篇 |
2004年 | 6917篇 |
2003年 | 6112篇 |
2002年 | 6062篇 |
2001年 | 7093篇 |
2000年 | 5373篇 |
1999年 | 4235篇 |
1998年 | 3563篇 |
1997年 | 3472篇 |
1996年 | 3294篇 |
1995年 | 3009篇 |
1994年 | 2952篇 |
1993年 | 3044篇 |
1992年 | 3151篇 |
1991年 | 3333篇 |
1990年 | 3084篇 |
1989年 | 3027篇 |
1988年 | 3066篇 |
1987年 | 2955篇 |
1986年 | 2800篇 |
1985年 | 3808篇 |
1984年 | 4005篇 |
1983年 | 3198篇 |
1982年 | 3410篇 |
1981年 | 3336篇 |
1980年 | 3230篇 |
1979年 | 3335篇 |
1978年 | 3422篇 |
1977年 | 3350篇 |
1976年 | 3448篇 |
1975年 | 3141篇 |
1974年 | 3150篇 |
1973年 | 3194篇 |
1972年 | 2235篇 |
1971年 | 1849篇 |
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
181.
Z. V. Golubenko A. S. Kamzin L. P. Ol’khovik M. M. Khvorov Z. I. Sizova V. P. Shabatin 《Physics of the Solid State》2002,44(9):1698-1702
Magnetization and remagnetization processes in a close-packed nanodispersed barium hexaferrite powder sample in the magnetically stable state were analyzed. Reversibility effects were discussed in terms of interparticle interaction. Judging from the magnetization curve and the parameters characterizing remagnetization irreversibility, the sample under study is a model system of small Stoner-Wohlfarth particles. 相似文献
182.
183.
D. P. Kouzov 《Journal of Mathematical Sciences》2002,108(5):721-735
A condition for regularization of boundary-contact integrals in two-dimensional problems of acoustics is considered. With an example of the simplest boundary-contact problem of acoustics, it is shown that a known sufficient condition for regularization is also a necessary one. The study of analytic properties of the transition admittance of an infinite plate that is in contact with a medium is conducted in order to obtain this statement. The considerations are carried out in general terms. The results obtained may be used in arbitrary models of plate theory, and they also may be adapted to boundary-contact problems of another physical nature. Bibliography: 9 titles. 相似文献
184.
185.
We discuss a mass change that has its origin in the action of forces on an object. This phenomenon, well-known in the context of quantum field theory (mass renormalization), can be discussed systematically in both classical and quantum mechanics in a framework given by Stückelberg. We employ this framework to resolve an interesting conflict of opinions between Schopenhauer and Hegel in the mid-19th century. We show that Hegel, Kant, and Schopenhauer demonstrated remarkable prescience in their views as seen from a modern perspective. 相似文献
186.
The results of experimental investigations on thermal nonequilibrium ionization in CO2: N2: He mixtures are presented. Measurements of electron density, ne, in vibrationally excited nitrogen were made in a supersonic flow with different CO2 contents as well as in a CO2: N2: He = 1 : 5 : 4 mixture laser gas. The mixtures were heated in a shock tube and expanded through a supersonic nozzle. Furthermore, supersonic mixing of N2 and CO2 + He was used in some experiments. The measured values of ne in the plenum chamber and in the supersonic nozzle are reported, and the processes responsible for nonequilibrium ionization in a laser-active medium are discussed. 相似文献
187.
188.
P. R. Latthe P. S. Shinge Bharati V. Badami P. B. Patil S. N. Holihosur 《Journal of Chemical Sciences》2006,118(3):249-256
3-[4-(Azidocarbonyl)]phenylsydnone (2) obtained from 3-(4-hydrazinocarbonyl) phenylsydnone (1) on Curtius rearrangement with alcohols, water and amines afforded the corresponding carbamates (3a-h), 4,4′-(sydnone-3-yl) diphenyl urea (4) and 4-(heterocyclyl)phenyl ureas (5a-l). Compounds (5a-l) on one-pot ring conversion yielded the 1,3,4-oxadiazolin-2-one derivatives (6a-l), which on reaction with N2H4 gave the 4-amino-1,2,4-triazolin-3-ones (7a-l). All these compounds exhibited moderate antimicrobial activity against the few microbes tested. The carbamates have been
found to be more toxic against fourth instar larvae ofAedes aegypti, in particular, then-butyl derivative (3e). 相似文献
189.
J.-C. Thomas L. Achouri J. Äystö R. Béraud B. Blank G. Canchel S. Czajkowski P. Dendooven A. Ensallem J. Giovinazzo N. Guillet J. Honkanen A. Jokinen A. Laird M. Lewitowicz C. Longour F. de Oliveira Santos K. Peräjärvi M. Stanoiu 《The European Physical Journal A - Hadrons and Nuclei》2004,21(3):419-435
190.
G.P. Romanelli D. Bennardi D.M. Ruiz G. Baronetti H.J. Thomas 《Tetrahedron letters》2004,45(48):8935-8939
Substituted coumarins are synthesized from phenols and β-ketoesters by the Pechmann reaction, using a Wells-Dawson heteropolyacid (H6P2W18O62·24H2O) as catalyst by a solvent-free procedure. This one requires low reaction times, 130 °C temperature and as little as 1 mol % of Wells-Dawson acid, obtaining good to excellent yields of coumarins. The catalyst showed to be reusable with no differences in the yields. The results are compared with those of the reactions performed in toluene solution. The presented synthetic procedure is a convenient, clean and fast alternative for synthesizing 4-substituted coumarins (17 examples). 相似文献