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   436421篇
  免费   4853篇
  国内免费   1234篇
化学   233972篇
晶体学   6489篇
力学   18783篇
综合类   13篇
数学   49985篇
物理学   133266篇
  2021年   3784篇
  2020年   4201篇
  2019年   4526篇
  2018年   5861篇
  2017年   5752篇
  2016年   8848篇
  2015年   5575篇
  2014年   8550篇
  2013年   20199篇
  2012年   15684篇
  2011年   19287篇
  2010年   13519篇
  2009年   13371篇
  2008年   17666篇
  2007年   17558篇
  2006年   16272篇
  2005年   14563篇
  2004年   13534篇
  2003年   11896篇
  2002年   11732篇
  2001年   13434篇
  2000年   10089篇
  1999年   7923篇
  1998年   6572篇
  1997年   6319篇
  1996年   6084篇
  1995年   5474篇
  1994年   5395篇
  1993年   5199篇
  1992年   5830篇
  1991年   5927篇
  1990年   5665篇
  1989年   5473篇
  1988年   5495篇
  1987年   5376篇
  1986年   5097篇
  1985年   6562篇
  1984年   6696篇
  1983年   5302篇
  1982年   5388篇
  1981年   5369篇
  1980年   4955篇
  1979年   5354篇
  1978年   5491篇
  1977年   5385篇
  1976年   5329篇
  1975年   4914篇
  1974年   4888篇
  1973年   4882篇
  1972年   3455篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Summary We report on neutron emission in palladium and titanium electrolitically charged with deuterium. The detection of neutrons is observed after thermal treatment of the electrode. In the hypothesis that neutrons came from cold fusion processes, we estimate a fusion rate as high as 1.3·10−21 fusions/deuteron pair/second.  相似文献   
992.
We present a model arising from the thermal modelling of two metal casting processes. We consider an enthalpy formulation for this two‐phase Stefan problem in a time varying three‐dimensional domain and consider convective heat transfer in the liquid phase. Then, we introduce a weak formulation in a fixed domain, by means of a suitable transformation. Existence of solution is obtained by applying an abstract theorem. The proof of this theorem is done by taking an implicit discretization in time together with a regularization. By passing to the limit in the regularization parameter and in the time step, we obtain the existence of solution of the continuous problem. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   
993.
We present here a tight-binding-like modelling of two-dimensional (2D) photonic crystals (PCs). Adopted from solid-state physics, the concept of generalized Wannier functions is used to construct a localized state basis that allows a parameter-free ab initio study of defects in PCs. We demonstrate here for a 2D triangular lattice of dielectric rods in air, the existence of this localized basis and the possibility to study large scale complex dielectric structures deviating from periodicity. Specific numerical simulations on a split waveguide embedded in this triangular lattice are performed, and they demonstrate the superiority of this method over plane wave based techniques.  相似文献   
994.
It is shown that the small-scale Rossby waves in a shallow rotating fluid placed in a gravitational field can generate large-scale zonal flows by means of a two-stream-like mechanism. This mechanism is revealed under the conditions when the Lighthill instability criterion is not satisfied. The text was submitted by the authors in English.  相似文献   
995.
We consider a class of Lagrangian theories where part of the coordinates does not have any time derivatives in the Lagrange function (we call such coordinates degenerate). We advocate that it is reasonable to reconsider the conventional definition of singularity based on the usual Hessian and, moreover, to simplify the conventional hamiltonization procedure. In particular, in such a procedure, it is not necessary to complete the degenerate coordinates with the corresponding conjugate momenta.  相似文献   
996.
The research presented here concerns the simultaneous grouping of the components of a vocal sound source. McAdams [J. Acoust. Soc. Am. 86, 2148-2159 (1989)] found that when three simultaneous vowels at different pitches were presented with subaudio frequency modulation, subjects judged them as being more prominent than when no vibrato was present. In a normal voice, when the harmonics of a vowel undergo frequency modulation they also undergo an amplitude modulation that traces the spectral envelope. Hypothetically, this spectral tracing could be one of the criteria used by the ear to group components of each vowel, which may help explain the lack of effect of frequency modulation coherence among different vowels in the previous study. In this experiment, two types of vowel synthesis were used in which the component amplitudes of each vowel either remained constant with frequency modulation or traced the spectral envelope. The stimuli for the experiment were chords of three different vowels at pitch intervals of five semitones (ratio 1.33). All the vowels of a given stimulus were produced by the same synthesis method. The subjects' task involved rating the prominence of each vowel in the stimulus. It was assumed that subjects would judge this prominence to be lower when they were not able to distinguish the vowel from the background sound. Also included as stimulus parameters were the different permutations of the three vowels at three pitches and a number of modulation conditions in which vowels were unmodulated, modulated alone, and modulated either coherently with, or independently of, the other vowels. Spectral tracing did not result in increased ratings of vowel prominence compared to stimuli where no spectral tracing was present. It would therefore seem that it has no effect on grouping components of sound sources. Modulated vowels received higher prominence ratings than unmodulated vowels. Vowels modulated alone were judged to be more prominent than vowels modulated with other vowels. There was, however, no significant difference between coherent and independent modulation of the three vowels. Differences among modulation conditions were more marked when the modulation width was 6% than when it was 3%.  相似文献   
997.
Limiting distributions are constructed for the log likelihood ratio of close hypotheses and for estimators from censored samples.Translated from Statisticheskie Metody Otsenivaniya i Proverki Gipotez, pp. 95–104, 1986.  相似文献   
998.
We consider a two-dimensional problem concerned with static deformation of an elastic halfstrip under the action of a self-equilibrated load at its end. A method is proposed for regularization of series over homogeneous solutions in the case of non-smooth prescribed loads. An example is given of a load for which divergence obtains for a series over homogeneous solutions for the stress field at the end of the halfstrip.Translated from Teoreticheskaya i Prikladnaya Mekhanika, No. 19, pp. 111–116, 1988.  相似文献   
999.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 50, No. 3, pp. 385–391, March, 1989.  相似文献   
1000.
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