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   217242篇
  免费   2436篇
  国内免费   754篇
化学   122714篇
晶体学   3407篇
力学   8370篇
综合类   4篇
数学   22572篇
物理学   63365篇
  2016年   2728篇
  2015年   2101篇
  2014年   2849篇
  2013年   9052篇
  2012年   6274篇
  2011年   7900篇
  2010年   5085篇
  2009年   5031篇
  2008年   7120篇
  2007年   7310篇
  2006年   7039篇
  2005年   6484篇
  2004年   5901篇
  2003年   5252篇
  2002年   5021篇
  2001年   6090篇
  2000年   4650篇
  1999年   3749篇
  1998年   2997篇
  1997年   3052篇
  1996年   3056篇
  1995年   2740篇
  1994年   2652篇
  1993年   2519篇
  1992年   2992篇
  1991年   2881篇
  1990年   2788篇
  1989年   2849篇
  1988年   2800篇
  1987年   2774篇
  1986年   2580篇
  1985年   3532篇
  1984年   3596篇
  1983年   2910篇
  1982年   3235篇
  1981年   3151篇
  1980年   3048篇
  1979年   3185篇
  1978年   3433篇
  1977年   3218篇
  1976年   3147篇
  1975年   2986篇
  1974年   2923篇
  1973年   2939篇
  1972年   1884篇
  1971年   1543篇
  1968年   2000篇
  1967年   2197篇
  1966年   1968篇
  1965年   1532篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
23.
A method using third order moments for estimating the regression coefficients as well as the latent state scores of the reduced-rank regression model when the latent variable(s) are non-normally distributed is presented in this paper. It is shown that the factor analysis type indeterminacy of the regression coefficient matrices is eliminated. A real life example of the proposed method is presented. Differences of this solution with the reduced-rank regression eigen solution are discussed.  相似文献   
24.
Exact closed-form solutions are exhibited for the Hopf equation for stationary incompressible 3D Navier-Stokes flow, for the cases of homogeneous forced flow (including a solution with depleted nonlinearity) and inhomogeneous flow with arbitrary boundary conditions. This provides an exact method for computing two- and higher-point moments, given the mean flow.  相似文献   
25.
The concepts of quasi-Chebyshev and weakly-Chebyshev and σ-Chebyshev were defined [3 - 7], andas a counterpart to best approximation in normed linear spaces, best coapprozimation was introduced by Franchetti and Furi^[1]. In this research, we shall define τ-Chebyshev subspaces and τ-cochebyshev subspaces of a Banach space, in which the property τ is compact or weakly-compact, respectively. A set of necessary and sufficient theorems under which a subspace is τ-Chebyshev is defined.  相似文献   
26.
J. H. Eberly 《Laser Physics》2006,16(6):921-926
We examine the application of Schmidt mode analysis to pure-state entanglement. Several examples permitting exact analytic calculation of Schmidt eigenvalues and eigenfunctions are included, as well as evaluation of the associated degree of entanglement.  相似文献   
27.
We show that the operations of permuting columns and rows separately and independently mix a square matrix in constant time. © 2006 Wiley Periodicals, Inc. Random Struct. Alg., 2006  相似文献   
28.
Non-stoichiometric ternary chalcogenides (Zn,Fe)S were prepared in the film form by pyrolytic spray deposition technique, using air/nitrogen as the carrier gas. The precursor solution comprised of ZnCl2, FeCl2 and thiourea. The depositions were carried out under optimum conditions of experimental parameters viz. carrier gas (air/nitrogen) flow rate, concentration of precursor constituents, nozzle substrate distance and temperature of quartz substrate. The deposited thin films were later sintered in argon at 1073 K for 120 min.The structural, compositional and optical properties of the sintered thin films were studied. X-ray diffraction studies of the thin films indicated the presence of (Zn,Fe)S solid solution with prominent cubic sphalerite phase while surface morphology as determined by scanning electron microscopy (SEM) revealed a granular structure.The chemical composition of the resulting thin films as analyzed by energy dispersive X-ray analysis (EDAX) reflected the composition of the precursor solutions from which the depositions were carried out with Fe at% values ranging from 0.4 up to 33.SEM micrographs of thin films reveal that the grain sizes of the thin films prepared using air as carrier gas and N2 as carrier gas are in the vicinity of 300 and 150 nm, respectively.The diffuse transmittance measurements for thin films, as a function of wavelength reveal the dependence of direct optical band gap on Fe content and type of phase.  相似文献   
29.
Ternary-phase ceramic system of Li2O Al2O3 4SiO2 doped with CuO, FeO and TiO2 has been prepared and subjected to dc electrical conductivity and thermally stimulated depolarization current (TSDC) measurements as a function of temperature (30-250 °C) and field strength. The electrical conductivity results are explained by assuming both ionic and electronic conduction mechanisms coexist with different contributions over the whole temperature range of experiments. TSDC spectra have been found to be characterized by a broad intense relaxation peak, which can be attributed to an ionic charge polarization. The broad relaxation transitions are apparently a result of the nonuniform nature of this process. Activation energies are calculated for both dc electrical conductivity and TSDC according to Arrhenius equation and initial rise method, respectively.  相似文献   
30.
Franz  H.  Asthalter  T.  Dommach  M.  Ehnes  A.  Messel  K.  Sergueev  I. 《Hyperfine Interactions》2002,141(1-4):131-134
The present status of the new nuclear resonance beamline PETRA 1 at HASYLAB, DESY, Hamburg is described. Besides an overview of the experimental setup some examples of recent experiments are given. Those cover the main applications, i.e., inelastic scattering from iron alloys and quasielastic scattering from glass-forming liquids. This revised version was published online in August 2006 with corrections to the Cover Date.  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