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   225736篇
  免费   4250篇
  国内免费   2002篇
化学   126621篇
晶体学   2764篇
力学   9279篇
综合类   105篇
数学   25252篇
物理学   67967篇
  2020年   2087篇
  2019年   2135篇
  2018年   2696篇
  2017年   2740篇
  2016年   3968篇
  2015年   2767篇
  2014年   3912篇
  2013年   9346篇
  2012年   8296篇
  2011年   10070篇
  2010年   7083篇
  2009年   6853篇
  2008年   9224篇
  2007年   9299篇
  2006年   8758篇
  2005年   7975篇
  2004年   7108篇
  2003年   6207篇
  2002年   6160篇
  2001年   6807篇
  2000年   5196篇
  1999年   3814篇
  1998年   3161篇
  1997年   3148篇
  1996年   2985篇
  1995年   2679篇
  1994年   2762篇
  1993年   2622篇
  1992年   2829篇
  1991年   2898篇
  1990年   2690篇
  1989年   2580篇
  1988年   2547篇
  1987年   2478篇
  1986年   2474篇
  1985年   3278篇
  1984年   3321篇
  1983年   2770篇
  1982年   3010篇
  1981年   2771篇
  1980年   2576篇
  1979年   2752篇
  1978年   2972篇
  1977年   3009篇
  1976年   3029篇
  1975年   2776篇
  1974年   2886篇
  1973年   2938篇
  1972年   2301篇
  1971年   1825篇
排序方式: 共有10000条查询结果,搜索用时 63 毫秒
941.
The early evolution of gas chromatography in the former German Democratic Republic (GDR) is surveyed and instrument development is outlined, describing the most important models manufactured in the GDR. The organization of the Arbeitsgemeinschaft für Gas-Chromatographie (Working Group for GC) is chronicled and its activities are discussed. Subsequent parts of this article will deal with the six symposia organized by the Arbeitsgemeinschaft between 1958 and 1968.  相似文献   
942.
943.
Liquid chromatography-electrospray ionisation mass spectrometry was evaluated in the high-throughput analysis of microcystins and nodularins, cyanobacterial peptide hepatotoxins. Extracts originating from cyanobacterial strains and field material were separated on a 30 mm × 4 mm I.D. Merck Purospher STAR RP-18e column using a rapid gradient of aqueous formic acid and acetonitrile, ionised by electrospray technique and analysed on a Micromass Quattro II triple-quadrupole mass spectrometer operated in the selected ion recording (SIR) mode. The total analysis time per sample was 2.8 min corresponding to 514 samples a day. The system showed good robustness during a series of 320 repetitive injections of a field sample containing three major microcystins.  相似文献   
944.
We consider some initial-boundary value problems for the linear and nonlinear heat equation where the gradient of the solution is prescribed on the boundary. Assuming that a solution exists, we obtain bounds for the solution and its gradient by maximum principle arguments or by means of differential and integral inequalities.  相似文献   
945.
In this paper we investigate the distribution of the Heisenberg evolution of the number operator in the stochastic limit of the quantum electromagnetic field without dipole approximation. We prove that in this case the usual Poisson statistics of the free fields has to be replaced by a hypergeometric series whose coefficients we compute explicitly. The physical effects of the new statistics should manifest themselves in situation which are not yet in the relativistic regime, but in which the dipole approximation is no longer valid. The text was submitted by the authors in English.  相似文献   
946.
A study is conducted of the relationship between the asymptotic behavior of a subharmonic function of finite order in a cone and the distribution of the measure associated with it.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 43, No. 2, pp. 247–261, Febraury, 1991.  相似文献   
947.
The instability of the rectilinear form of parallel weakly interacting dislocations, manifesting itself in their spontaneous wave-like bending, has been investigated. It is shown that softening of a crystal leads to the enhancement of this instability.  相似文献   
948.
A scheme of magnetic calorimeter for registration of rare events characterized by small energy release (cosmic rays, WIMPs, solitary X-ray quanta) is proposed. The calorimeter is brought to operation by adiabatic demagnetization, and its magnetic response is measured by a quantum interferometer (SQUID, A. Barone and G. Paterno, Physics and applications of Josephson Effect). Special consideration is given to the specific features of calorimeter operation in the ferromagnetic transition region. The trigger registration of ultrasmall energy release by a ferromagnetic system in the metastable state is described.  相似文献   
949.
The supersymetric path integrals in solving the problem of relativistic spinning particle interacting with pseudoscalar potentials is examined. The relative propagator is presented by means of path integral, where the spin degrees of freedom are described by odd Grassmannian variables and the gauge invariant part of the effective action has a form similar to the standard pseudoclassical action given by Berezin and Marinov. After integrating over fermionic variables (Grassmannian variables), the problem is reduced to a nonrelativistic one with an effective supersymetric potential. Some explicit examples are considered, where we have extracted the energy spectrum of the electron and the wave functions. PACS numbers: 03.65. Ca-Formalism, 03.65. Db-Functional analytical methods, 03.65. Pm-Relativistic wave equations.  相似文献   
950.
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