全文获取类型
收费全文 | 31855篇 |
免费 | 5580篇 |
国内免费 | 1695篇 |
专业分类
化学 | 4560篇 |
晶体学 | 569篇 |
力学 | 310篇 |
综合类 | 128篇 |
数学 | 1786篇 |
物理学 | 14087篇 |
无线电 | 17690篇 |
出版年
2024年 | 83篇 |
2023年 | 339篇 |
2022年 | 580篇 |
2021年 | 757篇 |
2020年 | 782篇 |
2019年 | 551篇 |
2018年 | 636篇 |
2017年 | 902篇 |
2016年 | 1030篇 |
2015年 | 1202篇 |
2014年 | 1844篇 |
2013年 | 2331篇 |
2012年 | 2333篇 |
2011年 | 2006篇 |
2010年 | 1627篇 |
2009年 | 1880篇 |
2008年 | 2203篇 |
2007年 | 2257篇 |
2006年 | 2053篇 |
2005年 | 1879篇 |
2004年 | 1572篇 |
2003年 | 1564篇 |
2002年 | 1243篇 |
2001年 | 1283篇 |
2000年 | 1067篇 |
1999年 | 861篇 |
1998年 | 704篇 |
1997年 | 659篇 |
1996年 | 552篇 |
1995年 | 484篇 |
1994年 | 432篇 |
1993年 | 349篇 |
1992年 | 271篇 |
1991年 | 210篇 |
1990年 | 142篇 |
1989年 | 110篇 |
1988年 | 76篇 |
1987年 | 53篇 |
1986年 | 40篇 |
1985年 | 47篇 |
1984年 | 38篇 |
1983年 | 12篇 |
1982年 | 24篇 |
1981年 | 16篇 |
1980年 | 10篇 |
1979年 | 7篇 |
1978年 | 4篇 |
1975年 | 6篇 |
1974年 | 7篇 |
1973年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
121.
122.
For vector quasivariational inequalities involving multifunctions in topological vector spaces, an existence result is obtained without a monotonicity assumption and with a convergence assumption weaker than semicontinuity. A new type of quasivariational inequality is proposed. Applications to quasicomplementarity problems and traffic network equilibria are considered. In particular, definitions of weak and strong Wardrop equilibria are introduced for the case of multivalued cost functions. 相似文献
123.
124.
125.
Consider a network where two routes are available for users wishing to travel from a source to a destination. On one route (which could be viewed as private transport) service slows as traffic increases. On the other (which could be viewed as public transport) the service frequency increases with demand. The Downs-Thomson paradox occurs when improvements in service produce an overall decline in performance as user equilibria adjust. Using the model proposed by Calvert [10], with a ⋅|M|1 queue corresponding to the private transport route, and a bulk-service infinite server queue modelling the public transport route, we give a complete analysis of this system in the setting of probabilistic routing. We obtain the user equilibria (which are not always unique), and determine their stability.AMS subject classification: 60K30, 90B15, 90B20, 91A10, 91A13This revised version was published online in June 2005 with corrected coverdate 相似文献
126.
Waveband switching (WBS) is a promising technique to reduce the switching and transmission costs in the optical domain of a wavelength-division multiplexing (WDM) network. This paper considers the problem of provisioning dynamic traffic using WBS in a WDM mesh network. The network of interest is a homogeneous WBS network, where each node has the functionality of WBS. The problem is called the dynamic WBS problem, which involves searching waveband-routes or wavelength-routes for the dynamically arriving traffic requests. The objective is to minimize the total switching and transmission costs in the optical domain. To solve the dynamic WBS problem, an auxiliary graph model capturing the network state is proposed. Based on the auxiliary graph, two heuristic on-line WBS algorithms with different waveband grouping policies are proposed, namely the wavelength-first WBS algorithm based on the auxiliary graph (WFAUG) and the waveband-first WBS algorithm based on the auxiliary graph (BFAUG). Simulation results indicate that WBS is an attractive technique which reduces the overall switching and transmission costs by up to 30% in the network. The results also show that the WFAUG algorithm outperforms the BFAUG algorithm in terms of port savings and cost savings. 相似文献
127.
An all-optical fiber nonlinear Fabry-Perot resonator is proposed. The steady-state model for describing this resonator is developed. The transmission and refection bistabilities are shown numerically. Our results show that the bistability in this system is similar to that in a normal nonlinear Fabry-Perot etalon, except that the characteristics of the bistability can be changed not only by the cavity length but also by the phase shifts of the fiber loop mirrors. 相似文献
128.
129.
We present a numerical implementation of the parallel gradient distribution (PGD) method for the solution of large-scale unconstrained optimization problems. The proposed parallel algorithm is characterized by a parallel phase which exploits the portions of the gradient of the objective function assigned to each processor; then, a coordination phase follows which, by a synchronous interaction scheme, optimizes over the partial results obtained by the parallel phase. The parallel and coordination phases are implemented using a quasi-Newton limited-memory BFGS approach. The computational experiments, carried out on a network of UNIX workstations by using the parallel software tool PVM, show that parallelization efficiency was problem dependent and ranged between 0.15 and 8.75. For the 150 problems solved by PGD on more than one processor, 85 cases had parallelization efficiency below 1, while 65 cases had a parallelization efficiency above 1. 相似文献
130.