全文获取类型
收费全文 | 3881篇 |
免费 | 695篇 |
国内免费 | 447篇 |
专业分类
化学 | 1155篇 |
晶体学 | 42篇 |
力学 | 444篇 |
综合类 | 97篇 |
数学 | 1632篇 |
物理学 | 1653篇 |
出版年
2024年 | 9篇 |
2023年 | 34篇 |
2022年 | 75篇 |
2021年 | 94篇 |
2020年 | 103篇 |
2019年 | 99篇 |
2018年 | 84篇 |
2017年 | 134篇 |
2016年 | 157篇 |
2015年 | 147篇 |
2014年 | 237篇 |
2013年 | 352篇 |
2012年 | 245篇 |
2011年 | 280篇 |
2010年 | 217篇 |
2009年 | 271篇 |
2008年 | 266篇 |
2007年 | 302篇 |
2006年 | 240篇 |
2005年 | 216篇 |
2004年 | 178篇 |
2003年 | 172篇 |
2002年 | 166篇 |
2001年 | 130篇 |
2000年 | 114篇 |
1999年 | 118篇 |
1998年 | 96篇 |
1997年 | 95篇 |
1996年 | 67篇 |
1995年 | 53篇 |
1994年 | 46篇 |
1993年 | 20篇 |
1992年 | 37篇 |
1991年 | 21篇 |
1990年 | 20篇 |
1989年 | 7篇 |
1988年 | 22篇 |
1987年 | 7篇 |
1986年 | 14篇 |
1985年 | 18篇 |
1984年 | 15篇 |
1983年 | 5篇 |
1982年 | 10篇 |
1981年 | 9篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1975年 | 2篇 |
1974年 | 2篇 |
1973年 | 2篇 |
排序方式: 共有5023条查询结果,搜索用时 140 毫秒
31.
Hu Haiyan 《Acta Mechanica Solida Sinica》1994,7(2):137-150
This paper deals with the numerical solution of high dimensional dynamic systems with nonsmooth characteristics, such as structural elastoplasticity, mechanical clearance and dry friction. As a stable periodic response of the system attracts its transient response, it may be extracted from the transient response somehow. The paper suggests a novel iteration scheme to extrapolate the periodic response from a short time history of its transient response by curve fitting. Compared with the current schemes such as shooting and incremental harmonic balancing, the present scheme makes full use of the information within the transient response and the system characters, then its computation efficiency has increased by an order and the numerical convergence depending on the initial iteration has greatly improved.The subject supported by the Chinese Foundation of Aeronautical Science 相似文献
32.
采用基于识别的分割方法进行手写数字串分割.在识别的过程中,运用反例样本估计分类器参数,实验数据表明,这种运用反例样本训练的分类器与没有经过反例样本训练的分类器相比,将提高拒识率到19%左右,从而保证了较高的识别率,验证了只有经过反例训练的分类器的输出结果才是可信赖的. 相似文献
33.
In this paper the sufficient conditions for the existence of positive solutions of the neutral difference equations with positive and negative coefficients are established. The results improve some known conclusions in the literature 相似文献
34.
P. G. Hjorth S. L. Kokkendorff S. Markvorsen 《Proceedings of the American Mathematical Society》2002,130(1):175-181
We study finite metric spaces with elements picked from, and distances consistent with, ambient Riemannian manifolds. The concepts of negative type and strictly negative type are reviewed, and the conjecture that hyperbolic spaces are of strictly negative type is settled, in the affirmative. The technique of the proof is subsequently applied to show that every compact manifold of negative type must have trivial fundamental group, and to obtain a necessary criterion for product manifolds to be of negative type.
35.
36.
Naoki Murabayashi 《Journal of Number Theory》2004,108(2):268-286
The purpose of this paper is to decide the conditions under which a CM elliptic curve is modular over its field of definition. 相似文献
37.
38.
The objective of this paper is a theoretical and numerical study of the dynamics of a taut inclined cable with a riding accolerating mass, which is suspended from two points of different elevation. The moving mass is a trolley that is accelerated by a solid fuel rocket down the inclined cable and is aerodynamically brought to a halt. The thrust of the rocket is tangential to the deformed configuration of the cable.Methods of analysis consist of the dynamics of small deformations superimposed on the static catenary state. The problem is nonlinear due to presence of friction and the convective acceleration interaction of the moving mass and the cable. Galerkin's procedure for removal of spatial dependence and numerical integration are used to obtain convergent solutions.Deceased 相似文献
39.
S. David Morley Raymond J. Abraham Ian S. Haworth David E. Jackson Martin R. Saunders Jeremy G. Vinter 《Journal of computer-aided molecular design》1991,5(5):475-496
Summary Four modifications to the COSMIC molecular mechanics force field are described, which greatly increase both its versatility and the accuracy of calculated conformational energies. The Hill non-bonded van der Waals potential function has been replaced by a two-parameter Morse curve and a new H-H potential, similar to that in MM3, incorporated. Hydrocarbon energies in particular are much improved.A simple iterative Hückel pi-electron molecular orbital calculation allows modelling of conjugated systems. Calculated bond lengths and rotational barriers for a series of conjugated hydrocarbons and nitrogen heterocycles are shown to be as accurate as those determined by the MM2 SCF method.Explicit hydrogen-bonding potentials for H-bond acceptor-donor atom pairs have been included to give better hydrogen bond energies and lengths. The van der Waals radii of protonic hydrogens are reduced to 0.5 Å and the energy well depth is increased to 1.0 kcal mol-1.Two new general atom types, N+
sp
2
and O-
sp
3
, have been introduced which allow a wide variety of charged conjugated systems to be studied. A minimum of parameterisation is required, as the new types are easily included in the Hückel scheme which automatically adjusts bond and torsional parameters according to the defined bond-order relationships. 相似文献
40.
The line search method incorporating the Wolfe conditions is modified to ensure that a descent algorithm terminates in a finite number of steps at an approximate stationary point where the second-order conditions of optimality are satisfied. A simple procedure based on conjugate directions is proposed to determine directions of negative curvature. 相似文献