全文获取类型
收费全文 | 21160篇 |
免费 | 2331篇 |
国内免费 | 1820篇 |
专业分类
化学 | 4866篇 |
晶体学 | 60篇 |
力学 | 876篇 |
综合类 | 177篇 |
数学 | 6466篇 |
物理学 | 4057篇 |
综合类 | 8809篇 |
出版年
2024年 | 53篇 |
2023年 | 149篇 |
2022年 | 325篇 |
2021年 | 396篇 |
2020年 | 481篇 |
2019年 | 477篇 |
2018年 | 418篇 |
2017年 | 551篇 |
2016年 | 682篇 |
2015年 | 616篇 |
2014年 | 999篇 |
2013年 | 1348篇 |
2012年 | 1192篇 |
2011年 | 1162篇 |
2010年 | 1036篇 |
2009年 | 1162篇 |
2008年 | 1197篇 |
2007年 | 1385篇 |
2006年 | 1286篇 |
2005年 | 1140篇 |
2004年 | 1064篇 |
2003年 | 930篇 |
2002年 | 853篇 |
2001年 | 795篇 |
2000年 | 719篇 |
1999年 | 675篇 |
1998年 | 559篇 |
1997年 | 492篇 |
1996年 | 501篇 |
1995年 | 394篇 |
1994年 | 358篇 |
1993年 | 298篇 |
1992年 | 296篇 |
1991年 | 235篇 |
1990年 | 205篇 |
1989年 | 178篇 |
1988年 | 139篇 |
1987年 | 116篇 |
1986年 | 97篇 |
1985年 | 59篇 |
1984年 | 62篇 |
1983年 | 19篇 |
1982年 | 44篇 |
1981年 | 25篇 |
1980年 | 27篇 |
1979年 | 33篇 |
1978年 | 13篇 |
1977年 | 18篇 |
1976年 | 14篇 |
1974年 | 10篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
61.
关于矩阵条件数的一些结论 总被引:4,自引:1,他引:3
陈德辉 《华东师范大学学报(自然科学版)》1986,(3)
本文讨论了一些矩阵范数达到极小的充要条件,其主要结果如下:1.设?为m×n实矩阵,且具有n个线性无关的列,则求?广义逆谱条件数等于1的充要条件为?=cI,其中c为正常数.2.设?为n阶非异实矩阵,则矩阵A的求逆p-范数条件数等于1的充要条件为A=cpσ,其中c为正常数,σ是置换阵,其对角元都等于 1或-1.3.设?为n阶非异实矩阵,则矩阵4的求逆F-范数条件数等于1的充要条件为?=cU,其中c为正常数,U为正交阵. 相似文献
62.
63.
Patrizio Frosini 《Geometriae Dedicata》2004,108(1):105-110
In this paper we prove that for every real-valued Morse function φ on a smooth closed manifold ℳ and every neighborhood U of its critical points a suitable Riemannian metric μ
U
exists such that φ is linear outside
U 相似文献
64.
This paper develops a theory for the global solution of nonconvex optimization problems with parameter-embedded linear dynamic systems. A quite general problem formulation is introduced and a solution is shown to exists. A convexity theory for integrals is then developed to construct convex relaxations for utilization in a branch-and-bound framework to calculate a global minimum. Interval analysis is employed to generate bounds on the state variables implied by the bounds on the embedded parameters. These bounds, along with basic integration theory, are used to prove convergence of the branch-and-bound algorithm to the global minimum of the optimization problem. The implementation of the algorithm is then considered and several numerical case studies are examined thoroughly 相似文献
65.
In this paper, we examine a variant of the uncapacitated lot-sizing model of Wagner–Whitin that includes fixed charges on the stocks. Such a model is natural in a production environment where stocking is a complex operation, and appears as a subproblem in more general network design problems.
Linear-programming formulations, a dynamic program, the convex hull of integer solutions and a separation algorithm are presented. All these turn out to be very natural extensions of the corresponding results of Barany et al. (Math. Programming Stud. 22 (1984) 32) for the uncapacitated lot-sizing problem. The convex hull proof is based on showing that an extended facility location formulation is tight and by projecting it onto the original space of variables. 相似文献
66.
67.
Some previous works show that symmetric fixed- and variable-stepsize linear multistep methods for second-order systems which do not have any parasitic root in their first characteristic polynomial give rise to a slow error growth with time when integrating reversible systems. In this paper, we give a technique to construct variable-stepsize symmetric methods from their fixed-stepsize counterparts, in such a way that the former have the same order as the latter. The order and symmetry of the integrators obtained is proved independently of the order of the underlying fixed-stepsize integrators. As this technique looks for efficiency, we concentrate on explicit linear multistep methods, which just make one function evaluation per step, and we offer some numerical comparisons with other one-step adaptive methods which also show a good long-term behaviour.
68.
L. D. Popov 《Central European Journal of Mathematics》2004,2(1):76-86
For a linear complementarity problem with inconsistent system of constraints a notion of quasi-solution of Tschebyshev type
is introduced. It’s shown that this solution can be obtained automatically by Lemke’s method if the constraint matrix of the
original problem is copositive plus or belongs to the intersection of matrix classes P
0 and Q
0. 相似文献
69.
The bias dependent interface charge is considered as the origin of the observed non-ideality in current–voltage and capacitance–voltage characteristics. Using the simplified model for the interface electronic structure based on defects interacting with the continuum of interface states, the microscopic origin of empirical parameters describing the bias dependent interface charge function is investigated. The results show that in non-ideal metal–semiconductor contacts the interface charge function depends on the interface disorder parameter, density of defects, barrier pinning parameter and the effective gap center. The theoretical predictions are tested against several sets of published experimental data on bias dependent ideality factor and excess capacitance in various metal–semicoductor systems. 相似文献
70.
分光光度法测定脯氨酸的含量 总被引:1,自引:0,他引:1
文章用分光光度法研究了脯氨酸与四氯对苯醌的荷移反应 .实验指出 ,在硼砂缓冲溶液中 ,脯氨酸与四氯对苯醌于 30℃的水浴中恒温 1 2 0 min,可形成 1∶ 1的稳定络合物 ,其λmax=35 8nm,表观摩尔吸光系数 ε=1 .5 0× 1 0 5L·mol- 1 ·cm- 1 ,在 60 ng·m L- 1 ~ 40 0 ng·m L- 1 的范围内符合比耳定律 ,用本方法测定药物制剂的含量与文献方法一致 ,回收率在 99.65 %~ 1 0 0 .7%范围内 ,相对标准偏差在 1 .4%以内 . 相似文献