全文获取类型
收费全文 | 404212篇 |
免费 | 4685篇 |
国内免费 | 1368篇 |
专业分类
电工技术 | 7572篇 |
综合类 | 316篇 |
化学工业 | 59963篇 |
金属工艺 | 16435篇 |
机械仪表 | 13491篇 |
建筑科学 | 8361篇 |
矿业工程 | 2154篇 |
能源动力 | 11534篇 |
轻工业 | 28477篇 |
水利工程 | 4273篇 |
石油天然气 | 7913篇 |
武器工业 | 17篇 |
无线电 | 49262篇 |
一般工业技术 | 83016篇 |
冶金工业 | 75140篇 |
原子能技术 | 9188篇 |
自动化技术 | 33153篇 |
出版年
2022年 | 2549篇 |
2021年 | 3891篇 |
2020年 | 2942篇 |
2019年 | 3806篇 |
2018年 | 6485篇 |
2017年 | 6482篇 |
2016年 | 6923篇 |
2015年 | 4320篇 |
2014年 | 7140篇 |
2013年 | 20049篇 |
2012年 | 11421篇 |
2011年 | 15274篇 |
2010年 | 12149篇 |
2009年 | 13720篇 |
2008年 | 14062篇 |
2007年 | 13822篇 |
2006年 | 12432篇 |
2005年 | 11132篇 |
2004年 | 10524篇 |
2003年 | 10434篇 |
2002年 | 9838篇 |
2001年 | 9746篇 |
2000年 | 9144篇 |
1999年 | 9540篇 |
1998年 | 24342篇 |
1997年 | 16731篇 |
1996年 | 12811篇 |
1995年 | 9532篇 |
1994年 | 8373篇 |
1993年 | 8392篇 |
1992年 | 6071篇 |
1991年 | 5701篇 |
1990年 | 5689篇 |
1989年 | 5322篇 |
1988年 | 5054篇 |
1987年 | 4432篇 |
1986年 | 4307篇 |
1985年 | 4821篇 |
1984年 | 4429篇 |
1983年 | 4001篇 |
1982年 | 3663篇 |
1981年 | 3737篇 |
1980年 | 3432篇 |
1979年 | 3331篇 |
1978年 | 3341篇 |
1977年 | 3756篇 |
1976年 | 4859篇 |
1975年 | 2851篇 |
1974年 | 2668篇 |
1973年 | 2736篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
A case of erysipeloid with bacteraemia caused by Erysipelothrix rhusiopathiae (ER) in a previously healthy 41-year old man is presented. The bacterium was probably introduced by the bite of a dog. He was treated successfully with penicillin V. The ER bacteraemia occurred without complications of endocarditis. 相似文献
192.
Saitoh T. Mattori S. Kinugawa S. Miyagi K. Taniguchi A. Kourogi M. Ohtsu M. 《Lightwave Technology, Journal of》1998,16(5):824-832
We report the modulation characteristics of a waveguide-type optical frequency comb generator (WG-OFCG) with the advantages of compactness, high modulation index and low driving power. The characteristics of the optical frequency comb (OFC) generated when the modulation index exceeds 2π are discussed. The power of the modulation sidebands was measured by the optical heterodyne method with an external-cavity laser as a local oscillator. The dependence of the modulation index of the WG-OFCG on the modulation frequency up to 40 GHz was measured. The generation span of the OFC at the modulation frequency detuned from an integer multiple of the free spectral range (FSR) is discussed 相似文献
193.
Clock stability characterization and measurement for telecommunications pose peculiar issues and requirements. This paper aims to provide an overview on this subject. After briefly recalling the background work, the key features and issues of clock stability characterization and measurement in telecommunications are described. The timing signal reference model and the stability quantities adopted in the new international standards are introduced and the impact of the measurement configuration and of the time error sampling period on their behavior are elucidated. The measurement of clock stability in telecommunications is then addressed, and a standard practical measurement procedure is outlined. Several measurement results are provided to support the concepts expounded with experimental evidence. The results shown have been chosen among those obtained throughout the last three years by testing clerks of digital switching exchanges, clocks for synchronous digital hierarchy (SDH) equipment, and state-of-the-art stand-alone slave clocks for synchronization networks. They thus represent a survey of the actual performance of clocks currently deployed in telecommunications networks 相似文献
194.
A simple technique for modeling transients in erbium-doped fiber amplifiers (EDFAs) has been applied to a gain-clamped amplifier. Integration of the variables along the length of the amplifier allows the formulation of the problem as a single simple, ordinary, time-dependent differential equation. We demonstrate examples for a typical conventional EDFA and one in which internal out-of-band oscillation is used to clamp the gain 相似文献
195.
196.
Salama H.F. Reeves D.S. Viniotis Y. 《Selected Areas in Communications, IEEE Journal on》1997,15(3):332-345
Multicast (MC) routing algorithms capable of satisfying the quality of service (QoS) requirements of real-time applications will be essential for future high-speed networks. We compare the performance of all of the important MC routing algorithms when applied to networks with asymmetric link loads. Each algorithm is judged based on the quality of the MC trees it generates and its efficiency in managing the network resources. Simulation results over random networks show that unconstrained algorithms are not capable of fulfilling the QoS requirements of real-time applications in wide-area networks. Simulations also reveal that one of the unconstrained algorithms, reverse path multicasting (RPM), is quite inefficient when applied to asymmetric networks. We study how combining routing with resource reservation and admission control improves the RPM's efficiency in managing the network resources. The performance of one semiconstrained heuristic, MSC, three constrained Steiner tree (CST) heuristics, Kompella, Pasquale, and Polyzos (1992), constrained adaptive ordering (CAO), and bounded shortest multicast algorithm (BSMA), and one constrained shortest path tree (CSPT) heuristic, the constrained Dijkstra heuristic (CDKS) are also studied. Simulations show that the semiconstrained and constrained heuristics are capable of successfully constructing MC trees which satisfy the QoS requirements of real-time traffic. However, the cost performance of the heuristics varies. The BSMA's MC trees are lower in cost than all other constrained heuristics. Finally, we compare the execution times of all algorithms, unconstrained, semiconstrained, and constrained 相似文献
197.
H. Nakamura M. Yoshinaga S. Nagashima A. Kato 《Journal of the European Ceramic Society》1996,16(12):1329-1335
Alumina-hydrate-coated SiC particles were prepared via a homogeneous precipitation method using urea, and the conditions for uniform coating and less coalescence of the particles were investigated. Coalescence of coated particles could be said to occur by collision and agglomeration followed by deposition of alumina hydrate on the agglomerated particles. Coalescence of coated particles was suppressed by use of low reaction temperature, low concentration of aluminium sulfate, high concentration of urea, intensive stirring, and a flow reactor. 相似文献
198.
Okabe S. Yorozuya T. Endo F. Yamagiwa T. Iwaasa S. 《Power Delivery, IEEE Transactions on》1992,7(3):1232-1238
The voltage-time characteristics of spacer surfaces for steep-front impulse waves are investigated under a particle-contaminated condition in SF6 gas. The characteristics are measured as a function of particle length, particle position, and space shapes. Flashover voltages monotonically increase in the submicrosecond region as time to flashover is shorter, and are a minimum in the 1 μs region. Applicability of the equal voltage-time area criterion for estimating the voltage-time characteristics is discussed and the estimation is clarified. Moreover, it is demonstrated that an optimized spacer with ribs greatly improves flashover voltages in the submicrosecond region as well as in the 1 μs and power frequency region 相似文献
199.
A value-based test is presented for economic screening of electric utility demand-side management (DSM) programs. The widely used least cost test is valid if the programs do not alter the amount or value of energy services provided to customers. But, in general, DSM programs have such effects and, as a result, the value consumers receive is changed. A more general economic efficiency test, the most value test, provides a practical method for considering the effects of DSM on customer value. The version presented allows for multiple load periods and can account for rate impacts on several customer classes. Four typical DSM programs are evaluated as illustrations 相似文献
200.