全文获取类型
收费全文 | 1319篇 |
免费 | 165篇 |
国内免费 | 101篇 |
专业分类
化学 | 225篇 |
晶体学 | 14篇 |
力学 | 171篇 |
综合类 | 54篇 |
数学 | 595篇 |
物理学 | 526篇 |
出版年
2024年 | 4篇 |
2023年 | 10篇 |
2022年 | 32篇 |
2021年 | 30篇 |
2020年 | 13篇 |
2019年 | 23篇 |
2018年 | 15篇 |
2017年 | 38篇 |
2016年 | 45篇 |
2015年 | 28篇 |
2014年 | 58篇 |
2013年 | 91篇 |
2012年 | 63篇 |
2011年 | 78篇 |
2010年 | 76篇 |
2009年 | 83篇 |
2008年 | 99篇 |
2007年 | 80篇 |
2006年 | 78篇 |
2005年 | 73篇 |
2004年 | 41篇 |
2003年 | 65篇 |
2002年 | 49篇 |
2001年 | 43篇 |
2000年 | 54篇 |
1999年 | 47篇 |
1998年 | 37篇 |
1997年 | 23篇 |
1996年 | 27篇 |
1995年 | 29篇 |
1994年 | 23篇 |
1993年 | 21篇 |
1992年 | 20篇 |
1991年 | 17篇 |
1990年 | 13篇 |
1989年 | 13篇 |
1988年 | 16篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有1585条查询结果,搜索用时 15 毫秒
111.
Liénard方程的比较原理 总被引:3,自引:0,他引:3
本文证明了一个比较原理,使方程x" f(x)x' g(x)=0的周期解存在性定理可以用来判断方程x" h(x,x')x' g(x)=0的周期解的存在性. 相似文献
112.
This paper is devoted to globally convergent methods for solving large sparse systems of nonlinear equations with an inexact approximation of the Jacobian matrix. These methods include difference versions of the Newton method and various quasi-Newton methods. We propose a class of trust region methods together with a proof of their global convergence and describe an implementable globally convergent algorithm which can be used as a realization of these methods. Considerable attention is concentrated on the application of conjugate gradient-type iterative methods to the solution of linear subproblems. We prove that both the GMRES and the smoothed COS well-preconditioned methods can be used for the construction of globally convergent trust region methods. The efficiency of our algorithm is demonstrated computationally by using a large collection of sparse test problems. 相似文献
113.
概述了图形图像处理系统中关于不规则区域的基本算法,包括:区域填充,边界跟踪,边界标志,几何处理,区域分割等等.并且,根据256色模式的特殊性,对传统的算法做了有针对性的改进,加快了处理速度,使其更适合于电影电视字幕、动画卡通人物等不规则图形图像区域.同时还给出了改进算法的程序设计的技巧. 相似文献
114.
The usual bifureation problems oeeurred in the study of the Planar differential systems having a region eonsisting of Periodie eycles are as follows:15 there any closed orbit whieh generates limit eyeles after a small perturbation?How many limit eyel 相似文献
115.
液固对流相变问题的焓式有限元法 总被引:1,自引:0,他引:1
本文基于焓的对流扩散方程,提出一种求解具有糊状区液固相变对流传热问题的有限元方法,避免了通常采用温度对流扩散方程进行数值求解所带来的许多困难,对问题的解决更加自然、简便。算例表明,本文提出的方法是有效且可行的。 相似文献
116.
In the present paper a finite layer method is studied for the elastodynamics of transverse isotropic bodies. With this method,
semi-infinite soils can be considered as an transverse isotropic half-space, its material functions varying with depth. Dividing
the half-space into a series of layers in the direction of depth, the material functions in each layer are simulated by exponential
functions. Consequently, the fundamental equations to be solved can be simplified if the Fourier transform with repsect to
coordinates is used. We have obtained the relationship between the “layer forces” and “layer displacements”. This finite layer
method, in fact, can also be called a semi-analytical method. It possesses those advantages as the usual semi-analytical methods
do, and can be used to analyse the problem of the interaction between soils and structures.
This paper is based on a portion of the author's dissertation submitted in partial fulfillment of the requirements of degree
of Ph. D. at the Shanghai Institute of Appl. Math. & Mech., Shanghai. 相似文献
117.
通过提出一种针对三维四面体网格的区域整形技术,给出了一种简便实用的四面体网格局部自适应加密方法,并将其与流量修正有限元法结合,应用于三维高速流的计算 相似文献
118.
The present analysis relates to the study of the full two-dimensional Brinkman equation representing the fluid flow through porous medium. The steady, incompressible fluid flow, with a negligible gravitational force, is constrained to flow in an infinitely long channel in which the height assumes a series of piecewise constant values. The control volume method is used to solve the Brinkman equation which involves the parameter, =/Da, where Da is the Darcy number and is the ratio of the fluid viscosity f to the effective viscosity
. An analytical study in the fully developed section of the composite channel is presented when the channel is of constant height and composed of several layers of porous media, each of uniform porosity. In the fully developed flow regime the analytical and numerical solutions are graphically indistinguishable. A geometrical configuration involving several discontinuities of channel height, and where the entry and exit sections are layered, is considered and the effect of different permeabilities is demonstrated. Further, numerical investigations are performed to evaluate the behaviour of fluid flow through regions which mathematically model some geological structures of various sizes, positions and permeability, for example a fault or a fracture, where the outlet channel is offset at different levels. The effect on the overall pressure gradient is also considered. 相似文献
119.
The two dimensional impinging circular twin-jet flow with no-cross flow is studied numerically and experimentally. The theoretical predications are carried out through numerical procedure based on finite volume method to solve the governing mass, momentum, turbulent kinetic energy and turbulent kinetic energy dissipation rate. The parameters studied were jet Reynolds number (9.5 × 104 Re 22.4 × 104), nozzle to plate spacing (3 h/d 12), nozzle to nozzle centerline spacing (l/d = 3, 5 and 8) and jet angle (0° θ 20°). It is concluded that the stagnation primary point moves away in the radial main flow direction by increasing the jet angle. This shift becomes stronger by increasing the nozzle to nozzle centerline spacing (l/d). A secondary stagnation point is set up between two jets. The value of pressure at this point decreases by decreasing Reynolds number and/or increasing the jet angle.
The sub atmospheric region occurs on the impingement plate. It increases strongly by increasing Reynolds number and decreases as the jet angle and/or a nozzle to plate spacing increases. The spreading of jet decreases by increasing nozzle to plate spacing. The intensity of re-circulation zone between two jets decreases by increasing of h/d and jet angle. The increase of turbulence kinetic energy occurs within high gradient velocity. 相似文献
120.
幂硬化介质中平面应力动态裂纹的尖端弹塑性场 总被引:1,自引:0,他引:1
本文采用塑性动力学方程,对幂硬化介质中平面应力动态裂纹尖端场进行了渐近分析,其结果表明:在裂纹尖端附近,应力具有的奇异性,应变具有的奇异性,其中A是一个与塑性区尺寸有关的常数因子,r是离开裂纹尖端的距离,n为硬化指数,文中给出了尖端场的控制参量D,它依赖于马赫数;并且给出了各物理量的角函数。 相似文献