全文获取类型
收费全文 | 56374篇 |
免费 | 8410篇 |
国内免费 | 6385篇 |
专业分类
化学 | 20727篇 |
晶体学 | 1231篇 |
力学 | 11903篇 |
综合类 | 745篇 |
数学 | 16586篇 |
物理学 | 19977篇 |
出版年
2024年 | 118篇 |
2023年 | 616篇 |
2022年 | 1229篇 |
2021年 | 1372篇 |
2020年 | 1845篇 |
2019年 | 1560篇 |
2018年 | 1570篇 |
2017年 | 2046篇 |
2016年 | 2481篇 |
2015年 | 1944篇 |
2014年 | 3058篇 |
2013年 | 4481篇 |
2012年 | 3594篇 |
2011年 | 3937篇 |
2010年 | 3327篇 |
2009年 | 3679篇 |
2008年 | 3584篇 |
2007年 | 3614篇 |
2006年 | 3311篇 |
2005年 | 3013篇 |
2004年 | 2625篇 |
2003年 | 2399篇 |
2002年 | 2041篇 |
2001年 | 1754篇 |
2000年 | 1684篇 |
1999年 | 1466篇 |
1998年 | 1385篇 |
1997年 | 1150篇 |
1996年 | 969篇 |
1995年 | 839篇 |
1994年 | 785篇 |
1993年 | 628篇 |
1992年 | 613篇 |
1991年 | 451篇 |
1990年 | 359篇 |
1989年 | 291篇 |
1988年 | 247篇 |
1987年 | 178篇 |
1986年 | 134篇 |
1985年 | 155篇 |
1984年 | 140篇 |
1983年 | 67篇 |
1982年 | 101篇 |
1981年 | 61篇 |
1980年 | 42篇 |
1979年 | 58篇 |
1978年 | 41篇 |
1977年 | 39篇 |
1976年 | 16篇 |
1957年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 546 毫秒
201.
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
202.
We demonstrate that a pair of additive quintic equations in at least 34 variables has a nontrivial integral solution, subject only to an 11-adic solubility hypothesis. This is achieved by an application of the Hardy–Littlewood method, for which we require a sharp estimate for a 33.998th moment of quintic exponential sums. We are able to employ p-adic iteration in a form that allows the estimation of such a mean value over a complete unit square, thereby providing an approach that is technically simpler than those of previous workers and flexible enough to be applied to related problems. 相似文献
203.
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
204.
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
205.
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
206.
Many recent algorithmic approaches involve the construction of a differential equation model for computational purposes, typically
by introducing an artificial time variable. The actual computational model involves a discretization of the now time-dependent differential system, usually
employing forward Euler. The resulting dynamics of such an algorithm is then a discrete dynamics, and it is expected to be
“close enough” to the dynamics of the continuous system (which is typically easier to analyze) provided that small – hence
many – time steps, or iterations, are taken. Indeed, recent papers in inverse problems and image processing routinely report
results requiring thousands of iterations to converge. This makes one wonder if and how the computational modeling process
can be improved to better reflect the actual properties sought.
In this article we elaborate on several problem instances that illustrate the above observations. Algorithms may often lend
themselves to a dual interpretation, in terms of a simply discretized differential equation with artificial time and in terms
of a simple optimization algorithm; such a dual interpretation can be advantageous. We show how a broader computational modeling
approach may possibly lead to algorithms with improved efficiency.
AMS subject classification (2000) 65L05, 65M32, 65N21, 65N22, 65D18 相似文献
207.
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
208.
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
209.
为提高CCD摄像机的成像质量,同时使镜头结构紧凑、小型化,在大视场光学镜头的设计中,引入标准二次曲面和偶次非球面。根据初级像差理论,分析了非球面的位置、初始结构参数的求解规律。通过理论计算和ZEMAX光学设计软件的优化,给出工作波长为0.4~0.7μm、全视场角为80°,相对孔径为1∶1.5的镜头设计实例。该镜头由7块镜片组成,包括一个标准二次曲面和两个8次方非球面;在40lp/mm空间频率处的MTF值超过0.85,全视场畸变小于3%,像质优良 相似文献
210.
求解非线性方程的一个新方法 总被引:2,自引:0,他引:2
张艺 《宁波大学学报(理工版)》2002,15(3):55-57
提出了一种求解非线性方程的数值方法,此方法不需要导数的计算,其收敛阶与抛物线法相同,但计算量要比抛物线法小得多。 相似文献