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   10889篇
  免费   1565篇
  国内免费   582篇
化学   4425篇
晶体学   70篇
力学   1332篇
综合类   92篇
数学   2774篇
物理学   4343篇
  2024年   14篇
  2023年   97篇
  2022年   148篇
  2021年   251篇
  2020年   291篇
  2019年   319篇
  2018年   286篇
  2017年   331篇
  2016年   443篇
  2015年   354篇
  2014年   476篇
  2013年   1019篇
  2012年   553篇
  2011年   573篇
  2010年   475篇
  2009年   603篇
  2008年   623篇
  2007年   730篇
  2006年   634篇
  2005年   518篇
  2004年   489篇
  2003年   463篇
  2002年   415篇
  2001年   375篇
  2000年   378篇
  1999年   293篇
  1998年   341篇
  1997年   211篇
  1996年   189篇
  1995年   142篇
  1994年   150篇
  1993年   107篇
  1992年   91篇
  1991年   87篇
  1990年   53篇
  1989年   73篇
  1988年   57篇
  1987年   41篇
  1986年   35篇
  1985年   38篇
  1984年   51篇
  1983年   22篇
  1982年   36篇
  1981年   26篇
  1980年   23篇
  1979年   25篇
  1978年   23篇
  1977年   10篇
  1976年   14篇
  1973年   12篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Methods for estimation of dispersion effects in two‐level unreplicated factorial designs are studied. The consequences of non‐constant variance are discussed. A natural assumption concerning the form of the covariance of location effects leads to a particular normal model. Some linear combinations of the response variables are constructed in order to make a simple structure for inference. The precision of point estimators of dispersion effects, where one is based on experiments with replicates, are compared. A numerical example is given as an illustration of a test. Finally, estimations in fractional designs are described and discussed. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
992.
非参数克莱因计量经济联立模型   总被引:2,自引:0,他引:2  
将非参数回归模型的局部线性估计方法与传统联立方程模型估计方法相结合 ,首次提出了非参数计量经济联立模型的局部线性两阶段最小二乘估计并应用于著名的克莱因计量经济联立模型且与其线性联立模型进行了比较 .结果表明 ,线性克莱因计量经济联立模型是非参数克莱因计量经济联立模型的一个较好近似 .  相似文献   
993.
We prove that two Dubrovin–Novikov Hamiltonian operators are compatible if and only if one of these operators is the Lie derivative of the other operator along a certain vector field. We consider the class of flat manifolds, which correspond to arbitrary pairs of compatible Dubrovin–Novikov Hamiltonian operators. Locally, these manifolds are defined by solutions of a system of nonlinear equations, which is integrable by the method of the inverse scattering problem. We construct the integrable hierarchies generated by arbitrary pairs of compatible Dubrovin–Novikov Hamiltonian operators.  相似文献   
994.
In this paper we want to extend the results of pointwise analysis through wavelet transforms to the class of functions where the local fluctuation is bounded by any submultiplicative function. This generalizez the results obtained before in the well-known case of Hölder regularity.  相似文献   
995.
Summary A recently improved model capable of extracting the wind field from SAR imagery without the aid of ?sea truth? is applied to ERS-1 SAR data for the Mediterranean Sea. The model is based on the properties of the relationship between the first two moments of the probabilistic distribution function of SAR signals as well as on spectral analysis of the SAR signal itself.  相似文献   
996.
Ye  J.  Kojima  N.  Furuya  K.  Munakata  F.  Okada  A. 《Journal of Thermal Analysis and Calorimetry》2002,69(3):1031-1036
A micro-thermal analysis technique was applied to investigate advanced silicon nitride materials, which exhibit high thermal conductivity. Local thermal properties in the microstructure were evaluated, and the grain boundaries were observed to have lower thermal conductance than the Si3N4 grains. It was found that thermal conductance both in the grains and boundaries was lowered by the addition of the sintering aid Al2O3, which is soluble in Si3N4 grains. This indicates that high thermal conductivity in silicon nitride ceramics is achieved both by grain growth, leading to a reduction in boundary density, and by eliminating soluble elements in silicon nitride grains. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
997.
In developing a new method to measure the phase distribution of a light wave utilizing the adaptive control of the pupil function with a liquid crystal panel, the optimization procedure for the adaptive control is shown to improve when a local algorithm is adopted. The feasibility of the proposed system is confirmed by computer simulation as well as by some basic experiments.  相似文献   
998.
Borabenzene Derivatives. 25 [1]. Methylbis(1-methylboratabenzene)indium: Synthesis and Structure. An Example for the Variability of Soft Structural Parameters in the Crystalline Environment The new boratabenzene derivative InMe(C5H5BMe)2 has been synthesized from 2-(Me3Sn)C5H5BMe and InMe3. The compound proves fluxional on the nmr time scale with average C2v symmetry in solution. An x-ray structure determination shows the existence of four molecules in the asymmetric unit differing mainly in the bonding geometry of the metal atoms with respect to the eight symmetrically independent boratabenzene ligands. Thus the dynamical behaviour in solution is reflected in the solid state by the soft structural parameters of the indium-ring coordination, with their variability exceeding the standard deviations of the corresponding individual observations by an order of magnitude.  相似文献   
999.
We compute the surface correction to the density of states of a particle in a convex box subjected to a magnetic field. Applying these results to orbital magnetism, we find that at high temperatures or weak magnetic fields the surface magnetization is always paramagnetic, but oscillations appear at low temperatures. In two dimensions they can give very large paramagnetic contributions near integer values of the filling factor. Explicit formulas are given for the zero-field susceptibility and for samples with a cylindrical shape in arbitrary magnetic field.  相似文献   
1000.
Szymański  K.  SatuŁa  D.  Dobrzyński  L. 《Hyperfine Interactions》2004,159(1-4):21-27
Nuclear resonance studies of the two different types impurity doped potassium hexachloro-stannates, the isomorphic system such as (K–Rb)2SnCl6 and K2(Sn–Re)Cl6 and the nonisomorphic system K2SnCl6:Al3+ in the high temperature cubic phase revealed contrasting features with one the other characterized by static in the former and dynamic feature in the latter case respectively. The resonance spectra of the nonisomorphic system indicate additionally a sign of the local structural transition above the conventional structural phase transition temperature. This seems to be triggered by the ligand-deficient octahedral defects and can be explained in terms of the enhanced activity of the octahedral defects for the hindered rotation.  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