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   723609篇
  免费   6333篇
  国内免费   2065篇
化学   365511篇
晶体学   10678篇
力学   36166篇
综合类   20篇
数学   96430篇
物理学   223202篇
  2021年   6531篇
  2020年   7007篇
  2019年   7914篇
  2018年   10609篇
  2017年   10877篇
  2016年   15141篇
  2015年   8545篇
  2014年   14185篇
  2013年   33116篇
  2012年   25478篇
  2011年   30462篇
  2010年   22591篇
  2009年   22537篇
  2008年   28417篇
  2007年   28104篇
  2006年   25760篇
  2005年   22945篇
  2004年   21301篇
  2003年   19109篇
  2002年   18979篇
  2001年   20983篇
  2000年   16021篇
  1999年   12482篇
  1998年   10637篇
  1997年   10404篇
  1996年   9744篇
  1995年   8705篇
  1994年   8651篇
  1993年   8345篇
  1992年   8954篇
  1991年   9500篇
  1990年   9063篇
  1989年   8934篇
  1988年   8553篇
  1987年   8509篇
  1986年   8117篇
  1985年   10362篇
  1984年   10784篇
  1983年   9021篇
  1982年   9310篇
  1981年   8734篇
  1980年   8425篇
  1979年   9038篇
  1978年   9276篇
  1977年   9115篇
  1976年   9041篇
  1975年   8675篇
  1974年   8511篇
  1973年   8808篇
  1972年   6321篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
111.
The method of equivalent variational methods, originally due to Carathéodory for free problems in the calculus of variations is extended to investigate feedback Nash equilibria for a class of n-person differential games. Both the finite-horizon and infinite-horizon cases are considered. Examples are given to illustrate the presented results.  相似文献   
112.
In the study of the behaviors of barriers in an enclosed field, one should take into account such phenomena as sound energy reflection, absorption, scattering and diffraction. Therefore, the study is much more difficult than that in free field. In this paper, sound barriers are classified into four kinds according to their size, number and shape. Each kind of barriers is modelled by a corresponding method based on a computer program—SOFIS. The program combines the ray-tracing technique and statistical method. The impulse response and some acoustical parameters such as sound pressure level at different positions can be calculated by the program, no matter there are a certain kind of barriers in the field or the field is empty. The ray-tracing program and the algorithms for various barriers are validated by the comparison between measurement and prediction of the reverberation room and the anechoic room of the Northwestern Polytechnic University.  相似文献   
113.
In this paper a new state called odd-excited binomial state (OEBS) is introduced. It interpolates between the odd number state and the odd-excited coherent state. We discuss some statistical properties, such as the Glauber second-order correlation function and squeezing phenomenon (normal and amplitude-squared squeezing) for this state. The quasiprobability distribution functions (Husimi Q-function and Wigner W-function) are also examined.  相似文献   
114.
The thermal decomposition of piperidine hydrothiocyanate, piperazine hydrothiocyanate, and the dihydrothiocyanates of ethylenediamine and 1,3-diaminopropane has been studied using TG. Piperidine hydrothiocyanate decomposes in a single step while the dihydrothiocyanates follow more complicated decomposition patterns yielding H2S and half of the organic moiety first. The second step involves the loss of H2S and the remainder of the organic moiety. In each case, complex polymeric materials result. Piperazine hydrothiocyanate also decomposes in two steps, the first involving the loss of half of the piperazine and the second involving the loss of piperazine and H2S. Kinetic parameters have been determined for all these reactions.  相似文献   
115.
116.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 5, pp. 815–819, May, 1991.  相似文献   
117.
A multidimensional generalization of the Reissner-Nordström solution of general relativity is obtained for the case of n Ricci-flat internal spaces. A two-parameter family of black-hole solutions for an arbitrary dimensionality D is selected. Nontrivial black holes with D > 4 are shown to exist only with a nonzero electric charge. Observational consequences are discussed, in particular, a violation of Coulomb's law.  相似文献   
118.
119.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 3, pp. 438–444, March, 1991.  相似文献   
120.
This article considers the splitting properties of finite-dimensional division rings over universal splitting fields of quadratic forms. An example of a field with u-invariant equal to 6 is constructed, which contradicts Kaplansky's conjecture concerning u-invariants.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im, V. A. Steklova Akademii Nauk SSSR, Vol. 175, pp. 75–89, 1989.  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