全文获取类型
收费全文 | 43497篇 |
免费 | 5855篇 |
国内免费 | 4233篇 |
专业分类
化学 | 11368篇 |
晶体学 | 968篇 |
力学 | 10138篇 |
综合类 | 618篇 |
数学 | 15103篇 |
物理学 | 15390篇 |
出版年
2024年 | 102篇 |
2023年 | 477篇 |
2022年 | 883篇 |
2021年 | 977篇 |
2020年 | 1235篇 |
2019年 | 1086篇 |
2018年 | 1115篇 |
2017年 | 1585篇 |
2016年 | 1784篇 |
2015年 | 1406篇 |
2014年 | 2321篇 |
2013年 | 3115篇 |
2012年 | 2661篇 |
2011年 | 3077篇 |
2010年 | 2589篇 |
2009年 | 2857篇 |
2008年 | 2762篇 |
2007年 | 2763篇 |
2006年 | 2542篇 |
2005年 | 2369篇 |
2004年 | 2007篇 |
2003年 | 1813篇 |
2002年 | 1611篇 |
2001年 | 1354篇 |
2000年 | 1279篇 |
1999年 | 1146篇 |
1998年 | 1047篇 |
1997年 | 886篇 |
1996年 | 727篇 |
1995年 | 627篇 |
1994年 | 573篇 |
1993年 | 455篇 |
1992年 | 465篇 |
1991年 | 364篇 |
1990年 | 290篇 |
1989年 | 220篇 |
1988年 | 187篇 |
1987年 | 131篇 |
1986年 | 90篇 |
1985年 | 116篇 |
1984年 | 110篇 |
1983年 | 55篇 |
1982年 | 70篇 |
1981年 | 51篇 |
1980年 | 27篇 |
1979年 | 43篇 |
1978年 | 34篇 |
1977年 | 38篇 |
1976年 | 14篇 |
1957年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
101.
L. Bergamaschi G. Gambolati G. Pini 《Journal of Computational and Applied Mathematics》2007,210(1-2):64-70
Integration of the subsurface flow equation by finite elements (FE) in space and finite differences (FD) in time requires the repeated solution to sparse symmetric positive definite systems of linear equations. Iterative techniques based on preconditioned conjugate gradients (PCG) are one of the most attractive tool to solve the problem on sequential computers. A present challenge is to make PCG attractive in a parallel computing environment as well. To this aim a key factor is the development of an efficient parallel preconditioner. FSAI (factorized sparse approximate inverse) and enlarged FSAI relying on the approximate inverse of the coefficient matrix appears to be a most promising parallel preconditioner. In the present paper PCG using FSAI, diagonal and pARMS (parallel algebraic recursive multilevel solvers) preconditioners is implemented on the IBM SP4/512 and CLX/768 supercomputers with up to 32 processors to solve underground flow problems of a large size. The results show that FSAI may allow for a parallel relative efficiency larger than 50% on the largest problems with p=32 processors. Moreover, FSAI turns out to be significantly less expensive and more robust than pARMS. Finally, it is shown that for p in the upper range may be much improved if PCG–FSAI is implemented on CLX. 相似文献
102.
等腰三角形Mindlin板的自由振动分析 总被引:2,自引:0,他引:2
提出了一种新方法来对基于 Mindlin剪切变形理论的等腰三角形板进行自由振动分析 .此方法采用了一种新的基函数并利用 pb-2 Rayleigh-Ritz边界函数得到了一种新型的 Ritz方法 .这种方法的有效性通过收敛性和对比性分析得到了证实 .数值结果表明此方法相当精确有效 . 相似文献
103.
B. M. Azizur Rahman A. K. M. Saiful Kabir Muttukrishnan Rajarajan Kenneth T. V. Grattan 《Optical and Quantum Electronics》2005,37(1-3):171-183
Modal solutions of planar photonic crystal waveguides with rectangular air-holes are presented by using a rigorous full-vectorial finite element-based approach. The effective indices, mode field profiles, spot-sizes, power confinements, modal hybridness, beat lengths and group velocity dispersions are shown for the fundamental and higher order modes of the quasi-TE and TM polarizations. 相似文献
104.
Yang Zuosheng 《国际流体数值方法杂志》2005,47(12):1423-1430
A complete boundary integral formulation for compressible Navier–Stokes equations with time discretization by operator splitting is developed using the fundamental solutions of the Helmholtz operator equation with different order. The numerical results for wall pressure and wall skin friction of two‐dimensional compressible laminar viscous flow around airfoils are in good agreement with field numerical methods. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
105.
Jose Manuel Corcuera Joao Guerra David Nualart Wim Schoutens 《Applied Mathematics and Optimization》2006,53(3):279-309
In this paper we consider the optimal investment problem in a market where the stock price process is modeled by a geometric
Levy process (taking into account jumps).
Except for the geometric Brownian model and the geometric Poissonian model, the
resulting models are incomplete and there are many equivalent martingale measures.
However, the model can be completed by the so-called power-jump assets. By doing this we allow investment in these new assets
and we can try to maximize the expected utility of these portfolios. As particular cases we obtain the optimal portfolios
based in stocks
and bonds, showing that the new assets are superfluous for certain martingale measures
that depend on the utility function we use. 相似文献
106.
We present a new verified optimization method to find regions for Hénon systems where the conditions of chaotic behaviour
hold. The present paper provides a methodology to verify chaos for certain mappings and regions. We discuss first how to check
the set theoretical conditions of a respective theorem in a reliable way by computer programs. Then we introduce optimization
problems that provide a model to locate chaotic regions. We prove the correctness of the underlying checking algorithms and
the optimization model. We have verified an earlier published chaotic region, and we also give new chaotic places located
by the new technique. 相似文献
107.
牛顿弦截法预估校正迭代格式的收敛阶 总被引:2,自引:0,他引:2
研究如下形式的牛顿弦截法的预估校正(P.C.)格式:P(预估):~xk+1=xk-(xk-xk-1)f(xk)f(xk)-f(xk-1)C(校正):xk+1=xk-(~xk+1-xk)f(xk)f~(xk+1)-f(xk)证明了它的收敛阶为2.618. 相似文献
108.
An infinite row of periodically spaced, identical rigid circularcylinders is excited by an acoustic line source which is parallelto the generators of the cylinders. A method for calculatingthe scattered field accurately and efficiently is presented.When the cylinders are sufficiently close together, Rayleigh–Blochsurface waves that propagate energy to infinity along the arrayare excited. An expression is derived which enables the amplitudesof these surface waves to be computed without requiring thesolution to the full scattering problem. 相似文献
109.
110.
电磁感应理论在磁悬浮列车中的应用 总被引:1,自引:1,他引:0
介绍了电磁感应和超导基本理论的实际应用-磁悬浮列车。以日本超导磁悬浮列车为例,阐述其作用原理,介绍了超导磁悬列车的发展状况。指出在物理教学中,理论学习与实际应用相结合是提高学生学习兴趣和培养创新能力的有效途径。 相似文献