全文获取类型
收费全文 | 9987篇 |
免费 | 1589篇 |
国内免费 | 915篇 |
专业分类
化学 | 3741篇 |
晶体学 | 71篇 |
力学 | 955篇 |
综合类 | 297篇 |
数学 | 3636篇 |
物理学 | 3791篇 |
出版年
2024年 | 37篇 |
2023年 | 151篇 |
2022年 | 530篇 |
2021年 | 431篇 |
2020年 | 317篇 |
2019年 | 268篇 |
2018年 | 230篇 |
2017年 | 405篇 |
2016年 | 443篇 |
2015年 | 372篇 |
2014年 | 632篇 |
2013年 | 825篇 |
2012年 | 622篇 |
2011年 | 604篇 |
2010年 | 526篇 |
2009年 | 595篇 |
2008年 | 554篇 |
2007年 | 606篇 |
2006年 | 503篇 |
2005年 | 430篇 |
2004年 | 398篇 |
2003年 | 381篇 |
2002年 | 362篇 |
2001年 | 273篇 |
2000年 | 294篇 |
1999年 | 270篇 |
1998年 | 223篇 |
1997年 | 213篇 |
1996年 | 162篇 |
1995年 | 117篇 |
1994年 | 126篇 |
1993年 | 102篇 |
1992年 | 70篇 |
1991年 | 64篇 |
1990年 | 58篇 |
1989年 | 31篇 |
1988年 | 34篇 |
1987年 | 29篇 |
1986年 | 40篇 |
1985年 | 31篇 |
1984年 | 26篇 |
1982年 | 17篇 |
1981年 | 11篇 |
1980年 | 8篇 |
1979年 | 16篇 |
1978年 | 10篇 |
1977年 | 14篇 |
1976年 | 5篇 |
1972年 | 5篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
A hybrid technique using constraint programming and linear programming is applied to the problem of scheduling with earliness and tardiness costs. The linear model maintains a set of relaxed optimal start times which are used to guide the constraint programming search heuristic. In addition, the constraint programming problem model employs the strong constraint propagation techniques responsible for many of the advances in constraint programming for scheduling in the past few years. Empirical results validate our approach and show, in particular, that creating and solving a subproblem containing only the activities with direct impact on the cost function and then using this solution in the main search, significantly increases the number of problems that can be solved to optimality while significantly decreasing the search time. 相似文献
82.
研究了Banach空间中拟-似变分包含解的存在与逼近问题.给出了一种寻求解的新的迭代算法,建立了具混合误差的Ishikawa型迭代序列强收敛到解的充要条件.所得结果推广了一些相关的结果. 相似文献
83.
Vladimir E. Bondarenko 《Complexity》2005,11(2):39-52
Information processing and two types of memory in an analog neural network model with time delay that produces chaos similar to the human and animal EEGs are considered. There are two levels of information processing in this neural network: the level of individual neurons and the level of the neural network. Similar to the state of brain, the state of chaotic neural network is defined. It is characterized by two types of memories (memory I and memory II) and correlation structure between the neurons. In normal (unperturbed) state, the neural network generates chaotic patterns of averaged neuronal activities (memory I) and patterns of oscillation amplitudes (memory II). In the presence of external stimulation, the activity patterns change, showing changes in both types of memory. As in experiments on stimulation of the brain, the neural network model shows synchronization of neuronal activities due to stimulus measured by Pearson's correlation coefficient. An increase in neural network asymmetry (increase of the neural network excitability) leads to the phenomenon similar to the epilepsy. Modeling of brain injury, Parkinson's disease, and dementia is performed by removing and weakening interneuron connections. In all cases, the chaotic neural network shows a decrease of the degree of chaos and changes in both types of memory similar to those observed in experiments with healthy human subjects and patients with Parkinson's disease and dementia. © 2005 Wiley Periodicals, Inc. Complexity 11:39–52, 2005 相似文献
84.
85.
资源有限网络计划的PRWI启发式优化方法 总被引:1,自引:0,他引:1
本文在综合考虑了有资源约束的网络计划结构特征、资源强度、时间约束等方面因素的基础上,提出了一种新的资源优化的启发式优化方法—PRWI方法,并通过分析证明了该方法处理问题的效果较现有的其它方法好。 相似文献
86.
Andrew V. Goldberg Michael D. Grigoriadis Robert E. Tarjan 《Mathematical Programming》1991,50(1-3):277-290
Goldfarb and Hao (1990) have proposed a pivot rule for the primal network simplex algorithm that will solve a maximum flow problem on ann-vertex,m-arc network in at mostnm pivots and O(n
2
m) time. In this paper we describe how to extend the dynamic tree data structure of Sleator and Tarjan (1983, 1985) to reduce the running time of this algorithm to O(nm logn). This bound is less than a logarithmic factor larger than those of the fastest known algorithms for the problem. Our extension of dynamic trees is interesting in its own right and may well have additional applications.Research partially supported by a Presidential Young Investigator Award from the National Science Foundation, Grant No. CCR-8858097, an IBM Faculty Development Award, and AT&T Bell Laboratories.Research partially supported by the Office of Naval Research, Contract No. N00014-87-K-0467.Research partially supported by the National Science Foundation, Grant No. DCR-8605961, and the Office of Naval Research, Contract No. N00014-87-K-0467. 相似文献
87.
提出了一种用于修正光学神经网络硬件系统误差的虚拟神经网络模型,光学实验结果表明该网络能够有效地消除硬件系统误差对实验结果的影响。 相似文献
88.
In this paper, a model of translation gateway is proposed. The communications between IPv4 network and IPv6 network are realized by using the Microsoft intermediate driver technology in environment of Windows 2000. 相似文献
89.
We consider a class of non-linear mixed integer programs with n integer variables and k continuous variables. Solving instances from this class to optimality is an NP-hard problem. We show that for the cases with
k=1 and k=2, every optimal solution is integral. In contrast to this, for every k≥3 there exist instances where every optimal solution takes non-integral values.
Received: August 2001 / Accepted: January 2002?Published online March 27, 2002 相似文献
90.
We give an almost complete classification of ergodicity and transience conditions for a general multi-queue system with the
following features: arrivals form Poisson streams and there are various routing schemes for allocating arrivals to queues;
the servers can be configured in a variety of ways; completed jobs can feed back into the system; the exponential service
times and feedback probabilities depend upon the configuration of the servers (this model includes some types of multi-class
queueing system); switching between service regimes is instantaneous. Several different levels of control of the service regimes
are considered. Our results for the N-queue system require randomisation of service configurations but we have studied the two queue system in situations where
there is less control. We use the semi-martingale methods described in Fayolle, Malyshev and Menshikov [3] and our results
generalise Kurkova [8] and complement Foley and McDonald [4] and [5].
AMS 2000 subject classification: Primary: 90B22; Secondary: 60J10 90B15 相似文献