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   600223篇
  免费   4472篇
  国内免费   1651篇
化学   290442篇
晶体学   8308篇
力学   32294篇
综合类   17篇
数学   98017篇
物理学   177268篇
  2021年   5038篇
  2020年   5478篇
  2019年   6223篇
  2018年   18175篇
  2017年   18062篇
  2016年   17266篇
  2015年   6940篇
  2014年   10687篇
  2013年   23724篇
  2012年   21756篇
  2011年   31412篇
  2010年   21596篇
  2009年   21884篇
  2008年   26679篇
  2007年   28495篇
  2006年   18775篇
  2005年   17774篇
  2004年   16838篇
  2003年   15789篇
  2002年   14772篇
  2001年   14922篇
  2000年   11581篇
  1999年   8872篇
  1998年   7749篇
  1997年   7586篇
  1996年   7108篇
  1995年   6369篇
  1994年   6335篇
  1993年   6107篇
  1992年   6425篇
  1991年   6925篇
  1990年   6628篇
  1989年   6541篇
  1988年   6376篇
  1987年   6184篇
  1986年   5926篇
  1985年   7451篇
  1984年   7812篇
  1983年   6569篇
  1982年   6856篇
  1981年   6366篇
  1980年   6047篇
  1979年   6546篇
  1978年   6775篇
  1977年   6648篇
  1976年   6603篇
  1975年   6315篇
  1974年   6139篇
  1973年   6449篇
  1972年   4723篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
The interferometric intensity patterns from a 2D shearing interferometer are shown and discussed. The intensity patterns can be obtained in two different approaches incorporating differential and extended wavefront controlled displacements. The reliable directional sensitivity of this interferometer allows the optimization of the measurement parameters to estimate the wavefront of the intensity patterns by regularization techniques.  相似文献   
53.
A new solvent-free sample preparation method using silver trifluoroacetate (AgTFA) was developed for the analysis of low molecular weight paraffins and microcrystalline waxes by laser desorption/ionization time-of-flight mass spectrometry (LDI-TOFMS). Experiments show that spectral quality can be enhanced by dispersing AgTFA directly in liquid paraffins without the use of additional solvents. This preparation mixture is applied directly to the MALDI probe. Solid waxes could be examined by melting prior to analysis. The method also provides sufficiently reproducible spectra that peak area ratios between mono- and bicyclic alkane peaks indicated variations in the cycloalkane content of paraffin samples. Dehydrogenation of hydrocarbons observed during the desorption/ionization process was studied by analysis of alkane standards.  相似文献   
54.
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   
55.
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   
56.
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   
57.
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   
58.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 5, pp. 815–819, May, 1991.  相似文献   
59.
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   
60.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 3, pp. 438–444, March, 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