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   197785篇
  免费   2190篇
  国内免费   628篇
化学   109719篇
晶体学   3309篇
力学   7906篇
综合类   4篇
数学   19024篇
物理学   60641篇
  2016年   2295篇
  2015年   1712篇
  2014年   2435篇
  2013年   8005篇
  2012年   5374篇
  2011年   6754篇
  2010年   4499篇
  2009年   4439篇
  2008年   6143篇
  2007年   6308篇
  2006年   6076篇
  2005年   5557篇
  2004年   5084篇
  2003年   4540篇
  2002年   4407篇
  2001年   5823篇
  2000年   4432篇
  1999年   3544篇
  1998年   2782篇
  1997年   2825篇
  1996年   2777篇
  1995年   2551篇
  1994年   2428篇
  1993年   2329篇
  1992年   2832篇
  1991年   2703篇
  1990年   2639篇
  1989年   2668篇
  1988年   2605篇
  1987年   2617篇
  1986年   2419篇
  1985年   3326篇
  1984年   3341篇
  1983年   2756篇
  1982年   2964篇
  1981年   2887篇
  1980年   2807篇
  1979年   2955篇
  1978年   3198篇
  1977年   3016篇
  1976年   2935篇
  1975年   2802篇
  1974年   2748篇
  1973年   2770篇
  1972年   1774篇
  1971年   1483篇
  1968年   1936篇
  1967年   2139篇
  1966年   1928篇
  1965年   1502篇
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
871.
The Nambu-Jona-Lasinio model as a particular model of quark flavour dynamics is bosonized in the low-energy regime using a generalized heat kernel expansion with local mass scale. The resulting effective meson Lagrangian defines a chiral soliton model, the solutions of which show a partial restoration of chiral symmetry inside the soliton.  相似文献   
872.
In this paper, the nonfragile control problem for synchronization of a class of chaotic dynamical systems with controller gain variations is studied. Using the Lyapunov method and LMI (linear matrix inequality) technique, a criterion for the existence of the nonfragile controller for synchronization is derived in terms of LMI. To show the effectiveness of the proposed method, the control problem is applied to Genesio chaotic system.  相似文献   
873.
We present Hall effect measurements on highly oriented pyrolytic graphite that indicate the occurrence of the integer quantum-Hall-effect. The evidence is given by the observation of regular plateau-like structures in the field dependence of the transverse conductivity obtained in van der Pauw configuration. Measurements with the Corbino-disk configuration support this result and indicate that the quasi-linear and non-saturating longitudinal magnetoresistance in graphite is governed by the Hall effect in agreement with a recent theoretical model for disordered semiconductors.  相似文献   
874.
There is experimental evidence that the non-sphericity of certain atmospheric particles can cause scattering properties different from those predicted by standard Mie theory. Numerous studies indicate the need to consider the presence of non-spherical particles in modeling the optical properties of atmospheric aerosols. On the other hand, natural aerosols show a great variety of shapes, making difficult a realistic choice of a particle shape (or shape mixture) model. In this paper, we test a parameterization of the particle shape in the retrieval of size distribution, phase function, single scattering albedo and asymmetry parameter from direct and sky-radiance measurements. For this purpose we have substituted the Kernel based on the Mie theory included in the model SKYRAD.PACK by one derived for non-spherical particles. The method is applied under different atmospheric conditions, including Saharan dust outbreak, polluted and local mineral episodes. We compare the results with those obtained by the well known spheroids algorithm used in the AERONET network.  相似文献   
875.
876.
Speech deterioration in postlingually deafened adults   总被引:1,自引:0,他引:1  
Postlinngually deafened adults reading the Rainbow Passage differed from hearing-control subjects in producing greater pitch variability and mean pitch on stressed and unstressed vowels, greater fluctuations in pitch within sentences, less correlation of intrinsic pitch with vowel height and slower temporal parameters. When reading the Phonetic Inventory Sentences, they revealed less differentiation of place of articulation in fricative and plosive consonants. The present findings, taken together with those of longitudinal and implant studies, are applied to constraining models of the role of self hearing in the elaboration of speech.  相似文献   
877.
Photosystem II core antenna of blue-green algae Synechococcus isolated in gel was studied by optical hole burning spectroscopy at 4·2 K. Persistent holes were burned into fluorescence spectra throughout the region 680–696 nm. The hole width extrapolated to zero burning fluence yielded a value 1·0±0·2 cm–1. A theoretical interpretation of the hole profile in fluorescence is presented. The dependence of saturated hole depth on burning wavelength is related to inhomogeneous site distribution function.Authors would like to thank F. Vácha from the Dept. of Biochemistry, Faculty of Nature Sciences, Charles University, for the preparation of the samples.  相似文献   
878.
This paper considers a deterministic flow inn-dimensional space, perturbed by a Markov jump process with small variance. Asymptotic expansions are obtained for certain functionals of Feynman—Kac type, in powers of a small parameter representing a noise intensity. The methods are analytical rather than probabilistic.The research of the first author was partly supported by AFOSR under Contract No. 91-0116-0, by ONR under Contract No. N0014-83-K-0542, and by the Institute for Mathematics and Its Applications with funds provided by the NSF and ONR. The second author's research was partly supported by NSF under Contract No. DMS-8702537, and by the Institute for Mathematics and Its Applications with funds provided by the NSF and ONR.  相似文献   
879.
Summary Some simple ideas are used here to prove a theorem on generating functions for a certain class of q-polynomials. This general theorem is then applied to derive a fairly large number of known as well as new generating functions for the familiar q-analogues of various polynomial systems including, for example, the classical orthogonal polynomials of Hermite, Jacobi, and Laguerre. A number of other interesting consequences of the theorem are also discussed.  相似文献   
880.
The critical limit of the eight-vertex model eigenvectors obtained by means of the generalized Bethe Ansatz is shown to give the six-vertex eigenvectors as constructed in a previous paper by two of the authors. Furthermore, an explicit mapping is established between these eigenvectors and the usual Bethe Ansatz eigenvectors of the six-vertex model. This allows one to show that the indexv labeling the eight-vertex eigenstates becomes exactly the third component of the total spin in the critical limit.  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