全文获取类型
收费全文 | 428篇 |
免费 | 66篇 |
国内免费 | 5篇 |
专业分类
化学 | 24篇 |
晶体学 | 1篇 |
力学 | 7篇 |
综合类 | 51篇 |
数学 | 166篇 |
物理学 | 250篇 |
出版年
2023年 | 13篇 |
2022年 | 22篇 |
2021年 | 35篇 |
2020年 | 12篇 |
2019年 | 15篇 |
2018年 | 9篇 |
2017年 | 34篇 |
2016年 | 22篇 |
2015年 | 13篇 |
2014年 | 25篇 |
2013年 | 23篇 |
2012年 | 23篇 |
2011年 | 14篇 |
2010年 | 20篇 |
2009年 | 27篇 |
2008年 | 40篇 |
2007年 | 25篇 |
2006年 | 29篇 |
2005年 | 23篇 |
2004年 | 15篇 |
2003年 | 20篇 |
2002年 | 8篇 |
2001年 | 9篇 |
2000年 | 2篇 |
1999年 | 4篇 |
1998年 | 3篇 |
1996年 | 4篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1991年 | 3篇 |
1989年 | 1篇 |
1984年 | 2篇 |
1983年 | 1篇 |
排序方式: 共有499条查询结果,搜索用时 125 毫秒
91.
《Optimization》2012,61(6):1187-1201
ABSTRACTSeveral optimization problems of modifying the weight of vertices in rooted trees, some of which are special cases of the inverse 1-median problem, are solved. Such problems arise in Very Large Scale Integration (VLSI) design of hardware security circuits, circuit synchronization, and analog-to-digital converters. These problems require assigning costly hardware (demands) to the leaves of rooted trees. One common property of these problems is that a resource allocated to an internal node can be shared by the entire sub-tree emanated at the node. Two types of problems are studied here. (1) A tree node employs an addition operation and the demands at the leaves are obtained by summing the resources allocated to nodes along the root-to-leaf paths. A linear-time bottom-up algorithm is shown to minimize the total resources allocated to tree nodes. (2) A tree’s node employs a multiplication operation and the demands at the leaves are obtained by multiplying the resources allocated to nodes along the root-to-leaf paths. A bottom-up dynamic programming algorithm is shown to minimize the total resources allocated to the tree’s nodes. While the above problems are usually solved by design engineers heuristically, this paper offers optimal solutions that can be easily programmed in CAD tools. 相似文献
92.
基于城乡恩格尔系数、基尼系数、社会保障水平系数与城乡人口比,定义城镇、农村与合成的社会和谐系数.此定义考虑了中国的城乡二元结构的特殊国情,能够从经济学的层面较为精确地定量描述国家或地区的社会和谐状态,可用于横向和纵向比较. 相似文献
93.
Zhengjun Liu Min GongYongkang Dou Feng LiuShen Lin Muhammad Ashfaq AhmadJingmin Dai Shutian Liu 《Optics and Lasers in Engineering》2012,50(2):248-255
Based on Arnold transform and discrete fractional angular transform, a double image encryption algorithm is designed. Two original images are regarded as the amplitude and phase of a complex function. Arnold transform is introduced for scrambling the pixels at a local area of the complex function. Subsequently the changed complex function is converted by discrete fractional angular transform. The operations mentioned will be performed many times. The amplitude of final output complex function is the encrypted image and its phase is regarded as the key of encryption algorithm. The parameters of the two transforms serve as the additional keys for enhancing the security. Some numerical simulations have been done to validate the performance of this encryption scheme. 相似文献
94.
江西相山铀矿区与非铀矿区稻谷中天然放射性核素含量对比研究 总被引:2,自引:0,他引:2
文章对比分析研究了江西相山铀矿区和非铀矿区稻谷中天然放射性核素U和Th的含量特征。样品分别采自江西省相山铀矿区及远离铀矿区的抚州市郊丘陵水稻种植区。结果表明相山铀矿区稻谷中天然放射性核素U的含量显著高于非铀矿区的稻谷,铀矿区内稻谷中放射性核素U含量平均值是非铀矿区的5.30倍;但铀矿区内稻谷中放射性核素Th的含量却较非铀矿区稻谷含量低,仅为其Th含量的50%。另外,相山铀矿区内稻谷中放射性核素U和Th之间存在较为显著的线性关系,稻谷中放射性核素Th的含量随U含量的增加而升高。铀矿区内稻谷中放射性核素U含量显著高于非铀矿区的原因还有待于进一步深入研究,然而加强该领域的研究对于保证我国区域稻谷质量和食品安全是非常重要和有意义的。 相似文献
95.
HAN Lian-Fang CHEN Yue-Ming YUAN Hao 《理论物理通讯》2009,51(4):648-652
We propose a deterministic quantum secure direct two check photon sequences are used to check the securities of the communication protocol by using dense coding. The channels between the message sender and the receiver. The continuous variable operations instead of the usual discrete unitary operations are performed on the travel photons so that the security of the present protocol can be enhanced. Therefore some specific attacks such as denial-of-service attack, intercept-measure-resend attack and invisible photon attack can be prevented in ideal quantum channel. In addition, the scheme is still secure in noise channel. Furthurmore, this protocol has the advantage of high capacity and can be realized in the experiment. 相似文献
96.
数字电力系统(DPS)——新世纪电力系统科技发展方向 总被引:1,自引:0,他引:1
本文提出了数字电力系统(DPS)的概念,并对其主要功能、所需进行的基础研究工作以及如何实现等问题作了阐述。数字电力系统有助于实现电力系统的科学化管理和决策、系统状态实时评估与改善系统安全稳定性,制定和实行经济运行策略,对电力系统实施紧急控制和反事故控制等。本文还专门论述了建立数字电力系统所需的硬件支持问题。 相似文献
97.
基于Dempster-Shafer证据理论的信任评估模型 总被引:8,自引:0,他引:8
从网格的动态性、分布性、不确定性等特征出发,参考社会学的人际信任关系结构,提出了一种基于Dempster-Shafer证据理论(简称D-S理论)的信任评估模型.该模型根据网格节点间的历史交易记录,给出“直接信任”的形式化描述,建立网格节点信任推荐机制,并利用D-S理论对证据进行组合,从而得到“间接信任”.然后将直接信任和间接信任进一步组合为“综合信任”,从而有效实现信任信息的融合.将本文提出的信任度评估方法应用到调度算法中,结果证明了该信任模型的可行件和实用件. 相似文献
98.
Zhang-Dong Ye Dong Pan Zhen Sun Chun-Guang Du Liu-Guo Yin Gui-Lu Long 《Frontiers of Physics》2021,16(2):21503
Quantum secure direct communication provides a direct means of conveying secret information via quantum states among legitimate users. The past two decades have witnessed its great strides both theoretically and experimentally. However, the security analysis of it still stays in its infant. Some practical problems in this field to be solved urgently, such as detector efficiency mismatch, side-channel effect and source imperfection, are propelling the birth of a more impeccable solution. In this paper, we establish a new framework of the security analysis driven by numerics where all the practical problems may be taken into account naturally. We apply this framework to several variations of the DL04 protocol considering real-world experimental conditions. Also, we propose two optimizing methods to process the numerical part of the framework so as to meet different requirements in practice. With these properties considered, we predict the robust framework would open up a broad avenue of the development in the field. 相似文献
99.
100.
A DIRECT METHOD IN OPTIMAL PORTFOLIO AND CONSUMPTION CHOICE 总被引:7,自引:0,他引:7
WUZHEN XUWENSHENG 《高校应用数学学报(英文版)》1996,11(3):349-354
In this paper, we use a direct method to solve the optimal portfolio and consumption choice problem in the security market for a specific case, in which the utility function is of a given homogenous form, i.e. the so-called CRRA case. The idea comes from the completion technique ever used in LQ optimal control. 相似文献