全文获取类型
收费全文 | 4488篇 |
免费 | 468篇 |
国内免费 | 304篇 |
专业分类
化学 | 125篇 |
晶体学 | 4篇 |
力学 | 412篇 |
综合类 | 72篇 |
数学 | 4207篇 |
物理学 | 440篇 |
出版年
2024年 | 6篇 |
2023年 | 43篇 |
2022年 | 48篇 |
2021年 | 82篇 |
2020年 | 115篇 |
2019年 | 119篇 |
2018年 | 129篇 |
2017年 | 155篇 |
2016年 | 187篇 |
2015年 | 116篇 |
2014年 | 174篇 |
2013年 | 348篇 |
2012年 | 220篇 |
2011年 | 185篇 |
2010年 | 147篇 |
2009年 | 212篇 |
2008年 | 260篇 |
2007年 | 234篇 |
2006年 | 254篇 |
2005年 | 224篇 |
2004年 | 174篇 |
2003年 | 195篇 |
2002年 | 195篇 |
2001年 | 165篇 |
2000年 | 169篇 |
1999年 | 158篇 |
1998年 | 117篇 |
1997年 | 96篇 |
1996年 | 79篇 |
1995年 | 84篇 |
1994年 | 44篇 |
1993年 | 42篇 |
1992年 | 38篇 |
1991年 | 43篇 |
1990年 | 34篇 |
1989年 | 25篇 |
1988年 | 39篇 |
1987年 | 28篇 |
1986年 | 27篇 |
1985年 | 32篇 |
1984年 | 30篇 |
1983年 | 16篇 |
1982年 | 33篇 |
1981年 | 16篇 |
1980年 | 34篇 |
1979年 | 23篇 |
1978年 | 12篇 |
1977年 | 23篇 |
1976年 | 19篇 |
1975年 | 6篇 |
排序方式: 共有5260条查询结果,搜索用时 15 毫秒
131.
A constrained form of the Weber problem is formulated in which no path is permitted to enter a prespecified forbidden region of the plane. Using the calculus of variations the shortest path between two points which does not intersect is determined. If is unconstrained distance, we denote the shortes distance along a feasible path by . The constrained Weber problem is, then: given points and positive weights wj, j = 1,2,…,n, find a point such that is a minimum.An algorithm is formulated for the solution of this problem when is Euclidean distance and is a single circular region. Numerical results are presented. 相似文献
132.
关于两两NQD列的若干极限性质 总被引:32,自引:0,他引:32
本文讨论了两两NQD列的Marcinkiewicz型弱大数律及Jamison型加权和的强稳定性,指出了两两NQD列与独立列的一个本质性区别,从而提出了解决两两NQD旬几乎处处收敛和完全收敛的一种方式。 相似文献
133.
建立并讨论了一类含有一般模糊弹性约束的广义模糊变量线性规划问题.首先,简单介绍了结构元方法并对结构元加权排序中权函数表征决策者风险态度进行了深入分析.然后选取风险中性的决策者来定义序关系,应用Verdegay模糊线性规划方法将含一般模糊弹性约束的广义模糊变量线性规划转化经典的线性规划问题,简化了原问题的求解.最后通过数值算例进一步说明了该方法的有效性. 相似文献
134.
《Optimization》2012,61(5):743-754
In this paper the problem of estimation of an optimal replacement interval for a system which is minimally repaired at failures is studied. The problem is investigated both under a parametric and a nonparametric form of the failure intensity of the system. It is assumed that observational data from n systems are available. Some asymptotic results are shown. A graphical procedure for determining/estimating an optimal replacement interval is presented. The procedure is particularly valuable for sensitivity analyses, for example with respect to the costs involved. 相似文献
135.
Difference systems of sets (DSS) are combinatorial configurations that arise in connection with code synchronization. This paper proposes a new method to construct DSSs, which uses known DSSs to partition some of the cosets of Zv relative to subgroup of order k, where v = km is a composite number. As applications, we obtain some new optimal DSSs. 相似文献
136.
《随机分析与应用》2013,31(2):251-274
Abstract The purpose of this paper is to investigate pathwise stability for certain Hilbert space-valued stochastic evolution equations. We are especially interested in the robustness analysis of perturbed stochastic differential equations in infinite dimensions. Sufficient conditions are established to ensure the almost surely stable decay of the given stochastic systems. Lastly, a corollary and corresponding example are studied to illustrate our theory. 相似文献
137.
138.
Nikolaus M. Loening Barth‐Jan van Rossum Hartmut Oschkinat 《Magnetic resonance in chemistry : MRC》2012,50(4):284-288
In nuclear magnetic resonance spectroscopy, experimental limits due to the radiofrequency transmitter and/or coil means that conventional radiofrequency pulses (“hard pulses”) are sometimes not sufficiently powerful to excite magnetization uniformly over a desired range of frequencies. Effects due to nonuniform excitation are most frequently encountered at high magnetic fields for nuclei with a large range of chemical shifts. Using optimal control theory, we have designed broadband excitation pulses that are suitable for solid‐state samples under magic‐angle‐spinning conditions. These pulses are easy to implement, robust to spinning frequency variations, and radiofrequency inhomogeneities, and only four times as long as a corresponding hard pulse. The utility of these pulses for uniformly exciting 13C nuclei is demonstrated on a 900 MHz (21.1 T) spectrometer. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
139.
《Optimization》2012,61(5):677-687
We consider the problem of approximate minimax for the Bolza problem of optimal control. Starting from the method of dynamic programming (Bellman) we define the ?-value function to be the approximation for the value function being a solution to the Hamilton–Jacobi equation. 相似文献
140.
Fayou Zhao 《Mathematische Nachrichten》2012,285(10):1294-1298
Fu and Lu et al. 7 showed that the commutator $\mathcal {H}_{\beta ,b}$ generated by the fractional Hardy operator and a locally integrable function b is bounded on the homogenous Herz spaces if and only if b is a central bounded mean oscillation function. We show that their result is optimal by giving a counterexample. 相似文献