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   643956篇
  免费   4564篇
  国内免费   1669篇
化学   302906篇
晶体学   8728篇
力学   35759篇
综合类   17篇
数学   110868篇
物理学   191911篇
  2021年   5120篇
  2020年   5524篇
  2019年   6263篇
  2018年   20959篇
  2017年   21074篇
  2016年   18556篇
  2015年   7296篇
  2014年   10826篇
  2013年   23962篇
  2012年   23656篇
  2011年   36641篇
  2010年   24714篇
  2009年   25048篇
  2008年   31541篇
  2007年   35085篇
  2006年   19031篇
  2005年   21103篇
  2004年   18441篇
  2003年   17719篇
  2002年   15692篇
  2001年   15031篇
  2000年   11831篇
  1999年   8917篇
  1998年   7790篇
  1997年   7617篇
  1996年   7241篇
  1995年   6455篇
  1994年   6414篇
  1993年   6180篇
  1992年   6483篇
  1991年   6988篇
  1990年   6696篇
  1989年   6607篇
  1988年   6464篇
  1987年   6260篇
  1986年   6004篇
  1985年   7548篇
  1984年   7902篇
  1983年   6649篇
  1982年   6946篇
  1981年   6440篇
  1980年   6135篇
  1979年   6644篇
  1978年   6866篇
  1977年   6675篇
  1976年   6650篇
  1975年   6363篇
  1974年   6184篇
  1973年   6524篇
  1972年   4757篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
Electrochemical separation of lead-silver alloys into the constituents by thin-layer electrolysis in molten electrolytes, with bismuth as metal separator, is studied. It is proposed to determine the extent of component recovery by potentiometry.  相似文献   
92.
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   
93.
Data Envelopment Analysis (DEA) offers a piece-wise linear approximation of the production frontier. The approximation tends to be poor if the true frontier is not concave, eg in case of economies of scale or of specialisation. To improve the flexibility of the DEA frontier and to gain in empirical fit, we propose to extend DEA towards a more general piece-wise quadratic approximation, called Quadratic Data Envelopment Analysis (QDEA). We show that QDEA gives statistically consistent estimates for all production frontiers with bounded Hessian eigenvalues. Our Monte-Carlo simulations suggest that QDEA can substantially improve efficiency estimation in finite samples relative to standard DEA models.  相似文献   
94.
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   
95.
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   
96.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 5, pp. 815–819, May, 1991.  相似文献   
97.
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   
98.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 3, pp. 438–444, March, 1991.  相似文献   
99.
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   
100.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 4, pp. 535–540, October, 1991.  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