全文获取类型
收费全文 | 54064篇 |
免费 | 3789篇 |
国内免费 | 3319篇 |
专业分类
化学 | 25794篇 |
晶体学 | 461篇 |
力学 | 5754篇 |
综合类 | 771篇 |
数学 | 16996篇 |
物理学 | 11396篇 |
出版年
2024年 | 102篇 |
2023年 | 519篇 |
2022年 | 1221篇 |
2021年 | 1299篇 |
2020年 | 1373篇 |
2019年 | 1300篇 |
2018年 | 1184篇 |
2017年 | 1475篇 |
2016年 | 1895篇 |
2015年 | 1426篇 |
2014年 | 2173篇 |
2013年 | 3784篇 |
2012年 | 3002篇 |
2011年 | 2916篇 |
2010年 | 2595篇 |
2009年 | 3162篇 |
2008年 | 3197篇 |
2007年 | 3565篇 |
2006年 | 2946篇 |
2005年 | 2684篇 |
2004年 | 2537篇 |
2003年 | 2270篇 |
2002年 | 1804篇 |
2001年 | 1452篇 |
2000年 | 1396篇 |
1999年 | 1251篇 |
1998年 | 1160篇 |
1997年 | 1013篇 |
1996年 | 896篇 |
1995年 | 860篇 |
1994年 | 738篇 |
1993年 | 588篇 |
1992年 | 554篇 |
1991年 | 464篇 |
1990年 | 412篇 |
1989年 | 282篇 |
1988年 | 284篇 |
1987年 | 186篇 |
1986年 | 173篇 |
1985年 | 198篇 |
1984年 | 157篇 |
1983年 | 80篇 |
1982年 | 149篇 |
1981年 | 96篇 |
1980年 | 73篇 |
1979年 | 97篇 |
1978年 | 50篇 |
1977年 | 24篇 |
1976年 | 33篇 |
1972年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
M. Georgelin A. Pocheau 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(2):169-174
The polycrystalline perovskitelike manganese oxides La1-xAxMnO (A = Na, and K, ) have been fabricated by sol-gel technique. For all the compositions explored in this work, the average manganese oxidation
state is practically constant, at for A = Na, and for A = K, respectively. A close relationship is confirmed to hold between the Curie temperature (Tc) and the bond distance of Mn-O. Results of magnetic measurements show that these materials can be utilized as suitable candidates
for magnetic refrigerants with wide applied temperature span, for their significant entropy change and the easily tuned Curie
temperature.
Received: 12 September 1997 / Revised: 18 December 1997 / Accepted: 21 January 1998 相似文献
12.
We discuss an error estimation procedure for the global error of collocation schemes applied to solve singular boundary value problems with a singularity of the first kind. This a posteriori estimate of the global error was proposed by Stetter in 1978 and is based on the idea of Defect Correction, originally due to Zadunaisky. Here, we present a new, carefully designed modification of this error estimate which not only results in less computational work but also appears to perform satisfactorily for singular problems. We give a full analytical justification for the asymptotical correctness of the error estimate when it is applied to a general nonlinear regular problem. For the singular case, we are presently only able to provide computational evidence for the full convergence order, the related analysis is still work in progress. This global estimate is the basis for a grid selection routine in which the grid is modified with the aim to equidistribute the global error. This procedure yields meshes suitable for an efficient numerical solution. Most importantly, we observe that the grid is refined in a way reflecting only the behavior of the solution and remains unaffected by the unsmooth direction field close to the singular point. 相似文献
13.
14.
固体力学有限元体系的结构拓扑变化理论 总被引:2,自引:1,他引:1
本文是文[1]的继续.文[1]提出了杆件系统的结构拓扑变化理论和拓扑变化法本文将这一理论和方法推进到连续体有限元体系;且在此基础上揭示出有限元体系的一个新性质,称为基本位移之梯度的正交性定理,从而给出一套设计敏度的显式表达式,可直接用于计算. 相似文献
15.
Volker Elling. 《Mathematics of Computation》2006,75(256):1721-1733
A particular case of initial data for the two-dimensional Euler equations is studied numerically. The results show that the Godunov method does not always converge to the physical solution, at least not on feasible grids. Moreover, they suggest that entropy solutions (in the weak entropy inequality sense) are not well posed.
16.
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
17.
We consider the problem of maximizing a linear fractional function on the Pareto efficient frontier of two other linear fractional functions. We present a finite pivoting-type algorithm that solves the maximization problem while computing simultaneously the efficient frontier. Application to multistage efficiency analysis is discussed. An example demonstrating the computational procedure is included. 相似文献
18.
Robert S. Strichartz 《Proceedings of the American Mathematical Society》2002,130(3):805-817
Harmonic mappings from the Sierpinski gasket to the circle are described explicitly in terms of boundary values and topological data. In particular, all such mappings minimize energy within a given homotopy class. Explicit formulas are also given for the energy of the mapping and its normal derivatives at boundary points.
19.
A FUNDAMENTAL SOLUTION FOR THE LAPLACE OPERATOR ON THE QUATERNIONIC HEISENBERG GROUP 总被引:2,自引:0,他引:2
朱理 《数学物理学报(B辑英文版)》2002,22(3)
In this paper, the author studies the Laplace operator on the quaternionic Heisenberg group, construct a fundamental solution for it and use this solution to prove the Lp-boundedness and the weak (1-1) boundedness of certain singular convolution operators on the quaternionic Heisenberg group. 相似文献
20.
Milan Medved? 《Journal of Mathematical Analysis and Applications》2002,267(2):643-650
A criterion for the nonexplosion of solutions to semilinear evolution equations on Banach spaces is proved. The result is obtained by applying a modification of the Bihari type inequality to the case of a weakly singular nonlinear integral inequality. 相似文献