全文获取类型
收费全文 | 10080篇 |
免费 | 1634篇 |
国内免费 | 663篇 |
专业分类
化学 | 377篇 |
晶体学 | 9篇 |
力学 | 309篇 |
综合类 | 124篇 |
数学 | 357篇 |
物理学 | 1999篇 |
无线电 | 9202篇 |
出版年
2024年 | 60篇 |
2023年 | 141篇 |
2022年 | 208篇 |
2021年 | 268篇 |
2020年 | 291篇 |
2019年 | 184篇 |
2018年 | 205篇 |
2017年 | 331篇 |
2016年 | 408篇 |
2015年 | 404篇 |
2014年 | 705篇 |
2013年 | 662篇 |
2012年 | 737篇 |
2011年 | 766篇 |
2010年 | 581篇 |
2009年 | 545篇 |
2008年 | 645篇 |
2007年 | 705篇 |
2006年 | 682篇 |
2005年 | 590篇 |
2004年 | 519篇 |
2003年 | 479篇 |
2002年 | 391篇 |
2001年 | 353篇 |
2000年 | 273篇 |
1999年 | 213篇 |
1998年 | 184篇 |
1997年 | 125篇 |
1996年 | 143篇 |
1995年 | 117篇 |
1994年 | 108篇 |
1993年 | 71篇 |
1992年 | 72篇 |
1991年 | 53篇 |
1990年 | 45篇 |
1989年 | 31篇 |
1988年 | 29篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 13篇 |
1984年 | 12篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1979年 | 1篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1974年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
971.
DESIGN AND ANALYSIS OF INTEGRATED OPERATIONAL AMPLIFIER XD1531 WITH LOW NOISE AT LOW FREQUENCIES 总被引:1,自引:0,他引:1
Principles of design are described for the low frequency integrated operationalamplifler XD1531 with low noise. The procedures of design of both the circuit structure and the tran-sistor shape are considered. The first stage of the circuit is designed with the methods of low noise atlow frequencies. The measures which decrease noises, especially, the 1/f noise originating .from thesemiconductor surface state and defects, are used for the transistor structure design. With analysisand comparison to products here and abroad in characteristics, it is shown that XD1531 has a lowernoise index at low frequencies than others, and the effectiveness of design methods for bringing lownoises have been demonstrated. 相似文献
972.
Design considerations for an automotive magnetorheological brake 总被引:2,自引:0,他引:2
In this paper, design considerations for building an automotive magnetorheological (MR) brake are discussed. The proposed brake consists of multiple rotating disks immersed in a MR fluid and an enclosed electromagnet. When current is applied to the electromagnet, the MR fluid solidifies as its yield stress varies as a function of the magnetic field applied. This controllable yield stress produces shear friction on the rotating disks, generating the braking torque. In this work, practical design criteria such as material selection, sealing, working surface area, viscous torque generation, applied current density, and MR fluid selection are considered to select a basic automotive MR brake configuration. Then, a finite element analysis is performed to analyze the resulting magnetic circuit and heat distribution within the MR brake configuration. This is followed by a multidisciplinary design optimization (MDO) procedure to obtain optimal design parameters that can generate the maximum braking torque in the brake. A prototype MR brake is then built and tested and the experimental results show a good correlation with the finite element simulation predictions. However, the braking torque generated is still far less than that of a conventional hydraulic brake, which indicates that a radical change in the basic brake configuration is required to build a feasible automotive MR brake. 相似文献
973.
本文简单地分析了影响PCB特性阻抗的主要因素及特性阻抗板在工程设计与生产制程中的应用和控制要点。 相似文献
974.
矩形集成电路半解析热分析软件--BJX热分析软件的研制 总被引:1,自引:0,他引:1
半解析热分析法具有解析法的高精度,又具有数值法的较宽适用范围。编制出的计算软件具有分析时间短、操作简便、成本低廉等优点,可能成为下一代集成电路实际使用的热分析软件。 相似文献
975.
A new analog fuzzy logic controller implemented in CMOS technology is described. The chosen membership function generator keeps the needed area for the inference engine very small while giving a big flexibility in the configuration of the membership function. The proposed solution for defuzzification gives an additional area reduction over earlier implementations. High speed, low power fuzzy controller hardware make the chip appropriate for intelligent sensor application. Simulation results as well as test measurements are presented and discussed to illustrate the properties and robustness of the proposed circuit. 相似文献
976.
977.
A Mixed Heuristic for Circuit Partitioning 总被引:5,自引:0,他引:5
C. Gil J. Ortega M.G. Montoya R. Baños 《Computational Optimization and Applications》2002,23(3):321-340
As general-purpose parallel computers are increasingly being used to speed up different VLSI applications, the development of parallel algorithms for circuit testing, logic minimization and simulation, HDL-based synthesis, etc. is currently a field of increasing research activity. This paper describes a circuit partitioning algorithm which mixes Simulated Annealing (SA) and Tabu Search (TS) heuristics. The goal of such an algorithm is to obtain a balanced distribution of the target circuit among the processors of the multicomputer allowing a parallel CAD application for Test Pattern Generation to provide good efficiency. The results obtained indicate that the proposed algorithm outperforms both a pure Simulated Annealing and a Tabu Search. Moreover, the usefulness of the algorithm in providing a balanced workload distribution is demonstrated by the efficiency results obtained by a topological partitioning parallel test-pattern generator in which the proposed algorithm has been included. An extented algorithm that works with general graphs to compare our approach with other state of the art algorithms has been also included. 相似文献
978.
979.
给出了Ti扩散LiNbO_3条波导任意阶导模场分布的试探解.通过变分法分析,不但可以合理地确定其中的待定参数,而且也得到了相应导模传播常数的近似值.与扩展的有效折射率方法比较:这种解不但在函数形式上简单,待定常数确定方便,而且具有精度高的优点.还可以得到等效一维波导折射率分布的解析表达式. 相似文献
980.
提出了一个新颖的蔡氏对偶混沌电路,并进行了深入的理论研究和计算机仿真分析.得出了几点结论:1)此混沌电路元器件少,且与蔡氏混沌电路结构完全对偶.2)在确定的元器件参数条件下,电路出现双涡卷奇怪吸引子和丰富的混沌动力学行为.
关键词:
蔡氏对偶电路
奇怪吸引子
混沌 相似文献