首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   495794篇
  免费   2925篇
  国内免费   1072篇
化学   226752篇
晶体学   6992篇
力学   28994篇
综合类   9篇
数学   86230篇
物理学   150814篇
  2021年   3848篇
  2020年   4251篇
  2019年   5048篇
  2018年   17223篇
  2017年   17122篇
  2016年   15540篇
  2015年   5540篇
  2014年   8943篇
  2013年   17690篇
  2012年   17613篇
  2011年   26719篇
  2010年   18644篇
  2009年   19270篇
  2008年   22226篇
  2007年   24068篇
  2006年   14528篇
  2005年   13827篇
  2004年   13310篇
  2003年   12765篇
  2002年   12023篇
  2001年   11387篇
  2000年   9051篇
  1999年   6759篇
  1998年   6253篇
  1997年   6030篇
  1996年   5543篇
  1995年   5017篇
  1994年   5020篇
  1993年   4930篇
  1992年   5104篇
  1991年   5613篇
  1990年   5377篇
  1989年   5380篇
  1988年   5124篇
  1987年   5117篇
  1986年   4749篇
  1985年   5752篇
  1984年   6073篇
  1983年   5138篇
  1982年   5480篇
  1981年   5068篇
  1980年   4784篇
  1979年   5340篇
  1978年   5562篇
  1977年   5554篇
  1976年   5664篇
  1975年   5309篇
  1974年   5221篇
  1973年   5390篇
  1972年   4253篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
The nonlinear theory of thermally stimulated depolarization currents is developed. The theory explains the processes of hetero- and homocharge relaxation in complex crystals with hydrogen bonds and allows the relaxation oscillator parameters to be calculated using the quadratic approximation for the external electric field.  相似文献   
12.
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   
13.
    
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   
14.
Summary This paper presents some applications of cyclic voltammetry at the interface of two immiscible electrolyte solutions by means of an experimental set-up described in a former publication. When using special sample preparation good results are obtained for the determination of iodide and quinine in pharmaceutical products as well as for the determination of quinine in tonic water and dodecylsulfate in a tooth-salt.

Herrn Prof. Dr. Günther Tölg zum 60. Geburtstag gewidmet  相似文献   
15.
Crystalline materials that are transparent in the vacuum UV spectral region and currently used have been reviewed. Transmission of crystals of solid solutions with the fluorite structure Ca1?x R xF2+x (R = Sc, Y, La, Yb, Lu) in the UV and vacuum UV spectral regions has been investigated. It is shown that application of different methods of purification of fluorides from some impurities can significantly improve the optical quality of fluoride multicomponent crystals in the short-wavelength spectral region.  相似文献   
16.
17.
18.
19.
20.
Beloshapka  V. K. 《Mathematical Notes》2004,75(3-4):475-488
In previous papers by the present author, a machinery for calculating automorphisms, constructing invariants, and classifying real submanifolds of a complex manifold was developed. The main step in this machinery is the construction of a “nice” model surface. The nice model surface can be treated as an analog of the osculating paraboloid in classical differential geometry. Model surfaces suggested earlier possess a complete list of the desired properties only if some upper estimate for the codimension of the submanifold is satisfied. If this estimate fails, then the surfaces lose the universality property (that is, the ability to touch any germ in an appropriate way), which restricts their applicability. In the present paper, we get rid of this restriction: for an arbitrary type (n,K) (where n is the dimension of the complex tangent plane, and K is the real codimension), we construct a nice model surface. In particular, we solve the problem of constructing a nondegenerate germ of a real analytic submanifold of a complex manifold of arbitrary given type (n,K) with the richest possible group of holomorphic automorphisms in the given class.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号