全文获取类型
收费全文 | 6541篇 |
免费 | 533篇 |
国内免费 | 890篇 |
专业分类
化学 | 2763篇 |
晶体学 | 26篇 |
力学 | 498篇 |
综合类 | 80篇 |
数学 | 3320篇 |
物理学 | 1277篇 |
出版年
2024年 | 9篇 |
2023年 | 70篇 |
2022年 | 89篇 |
2021年 | 159篇 |
2020年 | 173篇 |
2019年 | 197篇 |
2018年 | 173篇 |
2017年 | 178篇 |
2016年 | 216篇 |
2015年 | 185篇 |
2014年 | 304篇 |
2013年 | 514篇 |
2012年 | 287篇 |
2011年 | 345篇 |
2010年 | 297篇 |
2009年 | 432篇 |
2008年 | 447篇 |
2007年 | 448篇 |
2006年 | 417篇 |
2005年 | 346篇 |
2004年 | 322篇 |
2003年 | 301篇 |
2002年 | 283篇 |
2001年 | 243篇 |
2000年 | 261篇 |
1999年 | 175篇 |
1998年 | 168篇 |
1997年 | 145篇 |
1996年 | 140篇 |
1995年 | 128篇 |
1994年 | 94篇 |
1993年 | 77篇 |
1992年 | 64篇 |
1991年 | 52篇 |
1990年 | 34篇 |
1989年 | 18篇 |
1988年 | 26篇 |
1987年 | 26篇 |
1986年 | 22篇 |
1985年 | 20篇 |
1984年 | 21篇 |
1983年 | 6篇 |
1982年 | 5篇 |
1981年 | 9篇 |
1980年 | 9篇 |
1979年 | 10篇 |
1978年 | 7篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1957年 | 1篇 |
排序方式: 共有7964条查询结果,搜索用时 31 毫秒
991.
基于多重工作休假的成批到达离散时间排队的性能分析 总被引:2,自引:0,他引:2
研究了一个成批到达的离散时间 Geom$^{[X]}$/Geom/1 多重工作休假排队. 首先,建立了模型的二维马尔可夫链,利用矩阵分析的方法, 导出了稳态队长复杂的概率母函数. 其次, 为了展示此模型与经典无休假Geom$^{[X]}$/Geom/1排队的联系, 给出稳态队长的随机分解结果. 尤其重要的是,发现了条件负二项分布的双参数加法定理, 利用这些结论,得到了矩母函数序下的稳态等待时间的上下界. 进一步,求出了平均队长和平均等待时间的上下界. 最后,提出一些数值例子以验证结论. 相似文献
992.
该文, 欲求在含有原点的区域D内亚纯函数之囿界, 其中使用熊庆来教授, 李国平教授的方法. 所得结果较熊庆来教授的结果更一般些, 因此较Valiron教授, Mllilloux教授的结果更一般些与精确些. 相似文献
993.
We consider a variant of the classical two median facility location problem on a tree in which vertices are allowed to have positive or negative weights. This problem was proposed by Burkard et al. in 2000 (R.E. Burkard, E. Çela, H. Dollani, 2-medians in trees with pos/neg-weights, Discrete Appl. Math. 105 (2000) 51-71). who looked at two objectives, finding the total minimum weighted distance (MWD) and the total weighted minimum distance (WMD). Their approach finds an optimal solution in O(n2) time and O(n3) time, respectively, with better performance for special trees such as paths and stars. We propose here an O(nlogn) algorithm for the MWD problem on trees of arbitrary shape. We also briefly discuss the WMD case and argue that it can be solved in time. However, a systematic exposition of the later case cannot be contained in this paper. 相似文献
994.
995.
4度Cayley图的Hamilton圈分解的新方法与理论证明 总被引:2,自引:0,他引:2
王艳芳 《纯粹数学与应用数学》2010,26(3):380-386
给出了"Hamilton圈侧枝循环"等四个定理.它揭示了Abel群上4度Cayley图的Hamilton圈分解的特点及规律.同时,提出了Hamilton圈上"单向通道"的"离合"理论.在此基础上给出了Abel群上4度Cayley图的Hamilton圈分解的新方法-"离合法",此方法具有简明、快捷、分解方案多的特点.另外,Hamilton圈"单向通道"的"离合"理论还为解决6度Cayley图的Hamilton圈分解奠定了理论基础. 相似文献
996.
I. V. Oseledets D. V. Savostyanov E. E. Tyrtyshnikov 《Numerical Linear Algebra with Applications》2010,17(6):935-952
We propose new tensor approximation algorithms for certain discrete functions related with Hartree–Fock/Kohn–Sham equations. Given a canonical tensor representation for the electron density function (for example, produced by quantum chemistry packages such as MOLPRO), we obtain its Tucker approximation with much fewer parameters than the input data and the Tucker approximation for the cubic root of this function, which is part of the Kohn–Sham exchange operator. The key idea is in the fast and accurate prefiltering of possibly large‐scale factors of the canonical tensor input. The new algorithms are based on the incomplete cross approximation method applied to matrices and tensors of order 3 and outperform other tools for the same purpose. First, we show that the cross approximation method is robust and much faster than the singular value decomposition‐based approach. As a consequence, it becomes possible to increase the resolution of grid and the complexity of molecules that can be handled by the Hartree–Fock chemical models. Second, we propose a new fast approximation method for f1/3(x, y, z), based on the factor prefiltering method for f(x, y, z) and certain mimic approximation hypothesis. Third, we conclude that the Tucker format has advantages in the storage and computation time compared with the ubiquitous canonical format. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
997.
考虑服务员在休假期间不是完全停止工作,而是以相对于正常工作时低些的速率服务顾客的M/M/1工作休假排队模型.在此模型基础上,笔者针对现实的M/M/1排队模型中可能出现的外来干扰因素,提出了带RCE(Removal of Customers at the End)抵消策略的负顾客M/M/1工作休假排队这一新的模型.服务规则为先到先服务.工作休假策略为空竭服务多重工作休假.抵消原则为负顾客一对一抵消队尾的正顾客,若系统中无正顾客时,到达的负顾客自动消失,负顾客不接受服务.使用拟生灭过程和矩阵几何解方法给出了系统队长的稳态分布,证明了系统队长和等待时间的随机分解结果并给出稳态下系统中正顾客的平均队长和顾客在系统中的平均等待时间. 相似文献
998.
In this paper the Hamiltonian matrix formulation of the Riccati equation is used to derive the reduced-order pure-slow and pure-fast matrix differential Riccati equations of singularly perturbed systems. These pure-slow and pure-fast matrix differential Riccati equations are obtained by decoupling the singularly perturbed matrix differential Riccati equation of dimension n1+n2 into the pure-slow regular matrix differential Riccati equation of dimension n1 and the pure-fast stiff matrix differential Riccati equation of dimension n2. A formula is derived that produces the solution of the original singularly perturbed matrix differential Riccati equation in terms of solutions of the pure-slow and pure-fast reduced-order matrix differential Riccati equations and solutions of two reduced-order initial value problems. In addition to its theoretical importance, the main result of this paper can also be used to implement optimal filtering and control schemes for singularly perturbed linear time-invariant systems independently in pure-slow and pure-fast time scales. 相似文献
999.
D. Tripathi 《Applied mathematics and computation》2010,215(10):3645-452
The paper presents the transportation of viscoelastic fluid with fractional Maxwell model by peristalsis through a channel under long wavelength and low Reynolds number approximations. The propagation of wall of channel is taken as sinusoidal wave propagation (contraction and relaxation). Homotopy perturbation method (HPM) and Adomian decomposition method (ADM) are used to obtain the analytical approximate solutions of the problem. The expressions of axial velocity, volume flow rate and pressure gradient are obtained. The effects of fractional parameters (α), relaxation time (λ1) and amplitude (?) on the pressure difference and friction force across one wavelength are calculated numerically for different particular cases and depicted through graphs. 相似文献
1000.
Abdul-Majid Wazwaz 《Applied mathematics and computation》2010,216(4):1304-1309
In this work, a combined form of the Laplace transform method with the Adomian decomposition method is developed for analytic treatment of the nonlinear Volterra integro-differential equations. The combined method is capable of handling both equations of the first and second kind. Illustrative examples will be examined to support the proposed analysis. 相似文献