全文获取类型
收费全文 | 13233篇 |
免费 | 980篇 |
国内免费 | 1509篇 |
专业分类
化学 | 2824篇 |
晶体学 | 27篇 |
力学 | 717篇 |
综合类 | 145篇 |
数学 | 3592篇 |
物理学 | 1670篇 |
综合类 | 6747篇 |
出版年
2024年 | 31篇 |
2023年 | 125篇 |
2022年 | 180篇 |
2021年 | 226篇 |
2020年 | 252篇 |
2019年 | 295篇 |
2018年 | 281篇 |
2017年 | 308篇 |
2016年 | 347篇 |
2015年 | 350篇 |
2014年 | 579篇 |
2013年 | 727篇 |
2012年 | 684篇 |
2011年 | 719篇 |
2010年 | 635篇 |
2009年 | 807篇 |
2008年 | 911篇 |
2007年 | 1072篇 |
2006年 | 1019篇 |
2005年 | 857篇 |
2004年 | 763篇 |
2003年 | 727篇 |
2002年 | 648篇 |
2001年 | 534篇 |
2000年 | 522篇 |
1999年 | 370篇 |
1998年 | 346篇 |
1997年 | 264篇 |
1996年 | 212篇 |
1995年 | 183篇 |
1994年 | 154篇 |
1993年 | 108篇 |
1992年 | 103篇 |
1991年 | 81篇 |
1990年 | 60篇 |
1989年 | 43篇 |
1988年 | 45篇 |
1987年 | 37篇 |
1986年 | 24篇 |
1985年 | 18篇 |
1984年 | 18篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 7篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1978年 | 7篇 |
1976年 | 5篇 |
1957年 | 2篇 |
1955年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
近年来,小波技术越来越成为一种有效的信号处理手段,本文介绍了小波分析在轴承故障诊断中的原理和应用。 相似文献
992.
介绍一种对模拟机器人弹性的6×6刚度和柔顺矩阵进行对角化的几何分解方法.采用螺旋理论,从三个正交的外载螺旋柔顺轴和三个正交的变形螺旋柔顺轴推导得一个相似变换,对角元素是线性及旋转柔顺和刚度的静态值.这与应力、应变及转动惯量的主轴和主值类似,证明了对非奇异及奇异情况,分解总是存在的,并给出了分解表达式. 相似文献
993.
Two new azo-perester compounds, di-tert-butyl-6,6′-azobis-(6-cyanoperoxyheptanoate) (6,6-di-tBu) and di-tert-amyl-6,6′-azobis-(6-cyanoperoxyheptanoate) (6,6-di-tAm), synthesized on the basis of 6,6′-azobis-(6-cyanoheptanoic acid) (ACHpA), were investigated for their use in the radical polymerization of styrene (S) and methyl methacrylate (MMA). Their characteristics are given, including chemical (IR spectra), thermal (DSC) and kinetic, i.e., thermal decomposition studied by volumetric and gas chromatographic methods. The rate constants and activation energies of the decomposition of both the azo and perester bonds were determined. The new azo-peresters were utilized to initiate the radical solution polymerizations of S and MMA at 60 °C. The kinetic parameters of the processes, i.e., polymerization rate and overall rate constant, were determined. Subsequently, the polymerization products were characterized by IR and DSC. It was found that the perester groups were present in the obtained polymers, and hence, the polymers are “active” for further polymerization. 相似文献
994.
995.
996.
This paper examines Benders decomposition for a useful class of variational inequality (VI) problems that can model, e.g., economic equilibrium, games or traffic equilibrium. The dual of the given VI is defined. Benders decomposition of the original VI is derived by applying a Dantzig–Wolfe decomposition procedure to the dual of the given VI, and converting the dual forms of the Dantzig–Wolfe master and subproblems to their primal forms. The master problem VI includes a new cut at each iteration, with information from the latest subproblem VI, which is solved by fixing the “difficult” variables at values determined by the previous master problem. A scalar parameter called the convergence gap is calculated at each iteration; a negative value is equivalent to the algorithm making progress in that the last master problem solution is made infeasible by the new cut. Under mild conditions, the convergence gap approaches zero in the limit of many iterations. With a more restrictive condition that still admits many useful models, a zero value of the convergence gap implies that the master problem has found a solution of the VI. A small model of competitive equilibrium of three commodities in two regions serves as an illustration. 相似文献
997.
The truncated singular value decomposition is a popular method for the solution of linear ill-posed problems. The method requires the choice of a truncation index, which affects the quality of the computed approximate solution. This paper proposes that an L-curve, which is determined by how well the given data (right-hand side) can be approximated by a linear combination of the first (few) left singular vectors (or functions), be used as an aid for determining the truncation index. 相似文献
998.
The homogeneous approximation property (HAP) for frames is useful in practice and has been developed recently. In this paper, we study the HAP for the continuous wavelet transform. We show that every pair of admissible wavelets possesses the HAP in L2 sense, while it is not true in general whenever pointwise convergence is considered. We give necessary and sufficient conditions for the pointwise HAP to hold, which depends on both wavelets and functions to be reconstructed. 相似文献
999.
O. Briant C. Lemaréchal Ph. Meurdesoif S. Michel N. Perrot F. Vanderbeck 《Mathematical Programming》2008,113(2):299-344
When a column generation approach is applied to decomposable mixed integer programming problems, it is standard to formulate
and solve the master problem as a linear program. Seen in the dual space, this results in the algorithm known in the nonlinear
programming community as the cutting-plane algorithm of Kelley and Cheney-Goldstein. However, more stable methods with better
theoretical convergence rates are known and have been used as alternatives to this standard. One of them is the bundle method;
our aim is to illustrate its differences with Kelley’s method. In the process we review alternative stabilization techniques
used in column generation, comparing them from both primal and dual points of view. Numerical comparisons are presented for
five applications: cutting stock (which includes bin packing), vertex coloring, capacitated vehicle routing, multi-item lot
sizing, and traveling salesman. We also give a sketchy comparison with the volume algorithm.
This research has been supported by Inria New Investigation Grant “Convex Optimization and Dantzig-Wolfe Decomposition”. 相似文献
1000.
A balanced vertex-coloring of a graph G is a function c from V(G) to {−1,0,1} such that ∑{c(v):v∈V(G)}=0. A subset U of V(G) is called a balanced set if U induces a connected subgraph and ∑{c(v):v∈U}=0. A decomposition V(G)=V1∪?∪Vr is called a balanced decomposition if Vi is a balanced set for 1≤i≤r.In this paper, the balanced decomposition number f(G) of G is introduced; f(G) is the smallest integer s such that for any balanced vertex-coloring c of G, there exists a balanced decomposition V(G)=V1∪?∪Vr with |Vi|≤s for 1≤i≤r. Balanced decomposition numbers of some basic families of graphs such as complete graphs, trees, complete bipartite graphs, cycles, 2-connected graphs are studied. 相似文献