全文获取类型
收费全文 | 15531篇 |
免费 | 1286篇 |
国内免费 | 878篇 |
专业分类
化学 | 3540篇 |
晶体学 | 62篇 |
力学 | 4774篇 |
综合类 | 197篇 |
数学 | 5804篇 |
物理学 | 3318篇 |
出版年
2024年 | 22篇 |
2023年 | 176篇 |
2022年 | 291篇 |
2021年 | 317篇 |
2020年 | 433篇 |
2019年 | 340篇 |
2018年 | 338篇 |
2017年 | 431篇 |
2016年 | 506篇 |
2015年 | 384篇 |
2014年 | 710篇 |
2013年 | 979篇 |
2012年 | 683篇 |
2011年 | 812篇 |
2010年 | 632篇 |
2009年 | 856篇 |
2008年 | 840篇 |
2007年 | 830篇 |
2006年 | 804篇 |
2005年 | 716篇 |
2004年 | 603篇 |
2003年 | 631篇 |
2002年 | 590篇 |
2001年 | 551篇 |
2000年 | 486篇 |
1999年 | 469篇 |
1998年 | 420篇 |
1997年 | 381篇 |
1996年 | 281篇 |
1995年 | 279篇 |
1994年 | 225篇 |
1993年 | 184篇 |
1992年 | 220篇 |
1991年 | 149篇 |
1990年 | 142篇 |
1989年 | 78篇 |
1988年 | 71篇 |
1987年 | 58篇 |
1986年 | 27篇 |
1985年 | 98篇 |
1984年 | 121篇 |
1983年 | 60篇 |
1982年 | 104篇 |
1981年 | 95篇 |
1980年 | 56篇 |
1979年 | 56篇 |
1978年 | 50篇 |
1977年 | 32篇 |
1976年 | 21篇 |
1973年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
61.
杨青 《高等学校计算数学学报(英文版)》2003,12(2)
The mathematical model of semiconductor devices is described by the initial boundary value problem of a system of three nonlinear partial differential equations. One equation in elliptic form is for the electrostatic potential; two equations of convection-dominated diffusion type are for the electron and hole concentrations. Finite volume element procedure are put forward for the electrostatic potential, while upwind 相似文献
62.
The system design must be started from the concept with low cost and high performance. In this point, the topological shape of the structure is very important in the view of the structural rigidities and light-weight design.In this paper, the optimization methodology is presented in the design stage of the large optical mirror. We obtain the optimal layout through the topology optimization and then design the details through the size or shape optimization for structural rigidity. 相似文献
63.
The article concerns heterojunction resonant cavity-enhanced (RCE) Schottky photodiodes with GaAs in the absorption layer. The quantum efficiency and linear pulse response have thoroughly been analysed. For the first time, the response of a heterojunction photodiode has been modelled by the phenomenological model for a two-valley semiconductor. The results obtained have shown that the satellite valleys, as well as the parasitic time constant, significantly influence the response and, accordingly, have to be taken into account when analysing and optimizing RCE photodetectors. 相似文献
64.
A finite element solution of the Navier-Stokes equations for steady flow under the magnetic effect through a double-branched two-dimensional section of a three-dimensional model of the canine aorta is discussed. The numerical scheme involves transforming the physical co-ordinates to a curvilinear boundary-fitted co-ordinate system. The shear stress at the wall is calculated for a Reynolds number of 1000 with the branch-to-main aortic flow rate ratio as a parameter. The results are compared with earlier works involving experimental data and found to be in reasonable qualitative agreement. The steady flow, shear stress and branch flow under the effect of a magnetic field have been discussed in detail. 相似文献
65.
P. Schlagheck A. Buchleitner 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(3):401-415
We provide a detailed quantum treatment of the spectral characteristics and of the dynamics of nondispersive two-electron
wave packets along the periodically driven, collinear frozen planet configuration of helium. These highly correlated, long-lived
wave packets arise as a quantum manifestation of regular islands in a mixed classical phase space, which are induced by nonlinear
resonances between the external driving and the unperturbed dynamics of the frozen-planet configuration. Particular emphasis
is given to the dependence of the ionization rates of the wave packet states on the driving field parameters and on the quantum
mechanical phase space resolution, preceded by a comparison of 1D and 3D life times of the unperturbed frozen planet. Furthermore,
we study the effect of a superimposed static electric field component, which, on the grounds of classical considerations,
is expected to stabilize the real 3D dynamics against large (and possibly ionizing) deviations from collinearity.
Received 7 November 2002 / Received in final form 2 December 2002 Published online 28 January 2003 相似文献
66.
杨青 《高校应用数学学报(A辑)》2002,17(3):353-362
热传导型半导体器件的瞬时状态由四个方程的非线性偏微分方程组的初边值问题所决定,其中电子位势方程是椭圆型的,电子和空穴浓度方程是对流扩散型的,温度方程为热传导型的。本文提出解这类问题的特征变网格有限元法,并进行了理论分析,在一定条件下,得到了某种意义下的最佳L^2误差估计结果。 相似文献
67.
68.
The main aim of this paper is to provide convergence analysis of Quasi-Wilson nonconforming finite element to Maxwell's equations under arbitrary quadrilateral meshes.The error estimates are derived,which are the same as those for conforming elements under conventional regular meshes. 相似文献
69.
根据广义Laguerre多项式的数学性质,导出了较为简单的三维各向同性谐振子径向矩阵元的普遍公式,并在这基础上计算了一些重要特殊情形的径向矩阵元: 矢径r整数次幂的平均值,电偶极跃迁矩阵元和电四极跃迁矩阵元.
关键词:
三维各向同性谐振子
径向矩阵元
广义Laguerre多项式
偶极跃迁
四极跃迁 相似文献
70.
This paper considers the weighted extended b-splines as basis function for finite element method in electromagnetics and compares with the standard finite element method applied to the two-point boundary value problems with different boundary conditions. This new approach, which provides more accurate results than standard finite element method, is presented to compare other numerical techniques and applied to one-dimensional electromagnetic problems. Computed results are compared with other numerical results in literature. 相似文献