全文获取类型
收费全文 | 53842篇 |
免费 | 6501篇 |
国内免费 | 5377篇 |
专业分类
化学 | 14343篇 |
晶体学 | 1023篇 |
力学 | 12960篇 |
综合类 | 761篇 |
数学 | 20600篇 |
物理学 | 16033篇 |
出版年
2024年 | 132篇 |
2023年 | 582篇 |
2022年 | 1042篇 |
2021年 | 1186篇 |
2020年 | 1500篇 |
2019年 | 1296篇 |
2018年 | 1320篇 |
2017年 | 1882篇 |
2016年 | 2046篇 |
2015年 | 1650篇 |
2014年 | 2702篇 |
2013年 | 3880篇 |
2012年 | 3054篇 |
2011年 | 3557篇 |
2010年 | 3009篇 |
2009年 | 3374篇 |
2008年 | 3314篇 |
2007年 | 3358篇 |
2006年 | 3098篇 |
2005年 | 2880篇 |
2004年 | 2530篇 |
2003年 | 2329篇 |
2002年 | 2076篇 |
2001年 | 1767篇 |
2000年 | 1683篇 |
1999年 | 1592篇 |
1998年 | 1426篇 |
1997年 | 1230篇 |
1996年 | 982篇 |
1995年 | 882篇 |
1994年 | 751篇 |
1993年 | 572篇 |
1992年 | 593篇 |
1991年 | 469篇 |
1990年 | 385篇 |
1989年 | 275篇 |
1988年 | 215篇 |
1987年 | 174篇 |
1986年 | 131篇 |
1985年 | 156篇 |
1984年 | 135篇 |
1983年 | 75篇 |
1982年 | 90篇 |
1981年 | 60篇 |
1980年 | 42篇 |
1979年 | 60篇 |
1978年 | 42篇 |
1977年 | 49篇 |
1976年 | 20篇 |
1957年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
63.
Asaf Levin 《Operations Research Letters》2004,32(6):530-534
Consider the following problem: given a ground set and two minimization objectives of the same type find a subset from a given subset-class that minimizes the first objective subject to a budget constraint on the second objective. Using Megiddo's parametric method we improve an earlier weakly polynomial time algorithm. 相似文献
64.
In this work, the effect of flexibility on the trajectory of a planar two-link manipulator is studied using integrated computer-aided design/analysis (CAD/CAE) procedures. The solid models and finite element models of the parts of the manipulator are created by using the CAD/CAE software I-DEAS. The assembly is defined, and knowing the payload and the end point trajectory, the velocities and accelerations of the parts, joint forces and driving torques are calculated using the rigid body dynamics. All the time dependent nodal forces acting on the parts including distributed gravity and inertia forces are created in files with the I-DEAS program file format. The finite element vibration analysis of the parts is performed by I-DEAS. The end point vibrations and the deviations from the rigid-body trajectory are analyzed for different types of end point acceleration curves. A circular trajectory is considered as an example. It is observed that the precision of the manipulator can be increased by testing different end point acceleration curves without changing the trajectory and the duration of the end point work. The procedure explained in this work can be used for this purpose successfully. 相似文献
65.
Riad Hassani Patrick Hild Ioan Ionescu 《Mathematical Methods in the Applied Sciences》2004,27(1):47-67
We consider the Signorini problem with Coulomb friction in elasticity. Sufficient conditions of non‐uniqueness are obtained for the continuous model. These conditions are linked to the existence of real eigenvalues of an operator in a Hilbert space. We prove that, under appropriate conditions, real eigenvalues exist for a non‐local Coulomb friction model. Finite element approximation of the eigenvalue problem is considered and numerical experiments are performed. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
66.
B. Szafran P. S
p J. Adamowski S. Bednarek 《Physica E: Low-dimensional Systems and Nanostructures》2003,18(4):523-529
We present a theoretical study of the charging spectra in natural and artificial atoms. We apply a model electrostatic potential created by a homogenously charged sphere. This model potential allows for a continuous passage from the Coulomb potential of the nucleus to parabolic confinement potential of quantum dots. We consider electron systems with N=1,…,10 electrons with the use of the Hartree–Fock method. We discuss the qualitative similarities and differences between the chemical potential spectrum of electron systems bound to nucleus and confined in quantum dots. 相似文献
67.
We consider a splitting finite-difference scheme for an initial-boundary value problem for a two-dimensional nonlinear evolutionary
equation. The problem is split into nonlinear and linear parts. The linear part is also split into locally one-dimensional
equations. We prove the convergence and stability of the scheme in L
2 and C norms.
Printed in Lietuvos Matematikos Rinkinys, Vol. 45, No. 3, pp. 413–434, July–September, 2005. 相似文献
68.
69.
本文用变换群理论对运动水平平板混合对流边界层流动的动量、能量和浓度扩散方程进行了分析,得到了与X4/(7-5n)成正比的壁面温度分布和浓度分布,同时壁面运动速度正比于X(3-n)/(7-5n)时存在相似性解.导出了相似性解方程,用四阶Runge-Kutta方法进行了计算,给出了Pr=0.72 和Sc,K1,K2,K3参数下的速度、温度和浓度分布,得出了各参数对流场、温度场的影响。 相似文献
70.
对一类变形的变分不等式:求,使得提出了一类投影收缩算法,并得到了该算法的收敛性及相关性质. 相似文献