全文获取类型
收费全文 | 567211篇 |
免费 | 6250篇 |
国内免费 | 1004篇 |
专业分类
电工技术 | 10514篇 |
综合类 | 466篇 |
化学工业 | 90149篇 |
金属工艺 | 23366篇 |
机械仪表 | 18519篇 |
建筑科学 | 12538篇 |
矿业工程 | 4312篇 |
能源动力 | 14461篇 |
轻工业 | 45798篇 |
水利工程 | 6947篇 |
石油天然气 | 14963篇 |
武器工业 | 39篇 |
无线电 | 60305篇 |
一般工业技术 | 116306篇 |
冶金工业 | 95599篇 |
原子能技术 | 14685篇 |
自动化技术 | 45498篇 |
出版年
2021年 | 5490篇 |
2019年 | 5279篇 |
2018年 | 9222篇 |
2017年 | 9430篇 |
2016年 | 9857篇 |
2015年 | 6040篇 |
2014年 | 10265篇 |
2013年 | 26138篇 |
2012年 | 15796篇 |
2011年 | 21111篇 |
2010年 | 16995篇 |
2009年 | 18839篇 |
2008年 | 19081篇 |
2007年 | 18778篇 |
2006年 | 16308篇 |
2005年 | 14756篇 |
2004年 | 14011篇 |
2003年 | 13698篇 |
2002年 | 13261篇 |
2001年 | 12857篇 |
2000年 | 12334篇 |
1999年 | 12017篇 |
1998年 | 27663篇 |
1997年 | 20046篇 |
1996年 | 15643篇 |
1995年 | 12007篇 |
1994年 | 10861篇 |
1993年 | 10616篇 |
1992年 | 8337篇 |
1991年 | 8105篇 |
1990年 | 7996篇 |
1989年 | 7764篇 |
1988年 | 7478篇 |
1987年 | 6750篇 |
1986年 | 6535篇 |
1985年 | 7390篇 |
1984年 | 6704篇 |
1983年 | 6437篇 |
1982年 | 5776篇 |
1981年 | 5899篇 |
1980年 | 5631篇 |
1979年 | 5737篇 |
1978年 | 5667篇 |
1977年 | 6180篇 |
1976年 | 7689篇 |
1975年 | 5110篇 |
1974年 | 4903篇 |
1973年 | 4980篇 |
1972年 | 4279篇 |
1971年 | 4038篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
K. A. Abdikalikov V. K. Zadiraka O. S. Kondratenko S. S. Mel'nikova 《Cybernetics and Systems Analysis》1991,27(3):414-419
A fast algorithm is proposed for estimating the auto- and cross-correlation functions of a large signal. The algorithm is based on the sectioning method by the fast Fourier transform. We determine the optimal length of the portion of data read from external memory into RAM which achieves Tmin—a minimum processing time. An estimate of Tmin is obtained.Translated from Kibernetika, No. 3, pp. 78–81, May–June, 1991. 相似文献
192.
193.
194.
195.
An examination is presented of three techniques used for the efficient computation of fields diffracted by a subreflector that has been shaped by geometrical optics synthesis. It is found that these techniques, which are based on the geometrical theory of diffraction (GTD), produce errors in the computed fields that are specific to shaped reflectors. These errors are examined for a reflector system shaped to produce maximum gain from a tapered feed illumination. The discrepancies are directly related to the caustic being located near an observation point of the GTD calculations. The errors found are localized, and they increase in magnitude as the caustic approaches the main reflector. In a general offset geometry, the location of the caustic may be located arbitrarily close to the main reflector given a prescribed output aperture distribution. For the specific case considered here-the common situation of shaping to produce maximum gain-the caustic is located near the edge of the main reflector and on the reflection shadow boundary. A local correction is derived which creates a uniform solution through the caustic and across the reflection shadow boundary. Away from this point the calculation recedes to the standard GTD solution 相似文献
196.
Shamansky H.T. Dominek A.K. Peters L. Jr. 《Antennas and Propagation, IEEE Transactions on》1989,37(8):1019-1025
The traveling-wave energy, which multiply diffracts on a straight thin wire, is represented as a sum of terms, each with a distinct physical meaning, that can be individually examined in the time domain. Expressions for each scattering mechanism on a straight thin wire are cast in the form of four basic electromagnetic wave concepts: diffraction, attachment, launch, and reflection. Using the basic mechanisms from P.Ya. Ufimtsev (1962), each of the scattering mechanisms is included into the total scattered field for the straight thin wire. Scattering as a function of angle and frequency is then compared to the moment-method solution. These analytic expressions are then extended to a lossy wire with a simple approximate modification using the propagation velocity on the wire as derived from the Sommerfeld wave on a straight lossy wire. Both the perfectly conducting and lossy wire solutions are compared to moment-method results, and excellent agreement is found. As is common with asymptotic solutions, when the electrical length of wire is smaller than 0.2 λ the results lose accuracy. The expressions modified to approximate the scattering for the lossy thin wire yield excellent agreement even for lossy wires where the wire radius is on the order of skin depth 相似文献
197.
Multifunctional logic modules consisting of elements with bilateral conductance are proposed; when realizing Boolean formulas in the basis {&;, v, !} consisting of at most six letters, these modules have no element redundancy. If the basis has more than six letters, then the redundancy does not exceed 33%. 相似文献
198.
Bloomfield R.E. Guerra S. Miller A. Masera M. Weinstock C.B. 《Security & Privacy, IEEE》2006,4(3):66-68
Critical systems are aptly named - from electric power to water and gas to the telephone system and the Internet, they're all critical to some aspect of our daily lives. We're a networked society and as such, it's important to both know whether critical systems are trustworthy and be able to communicate, review, and debate the level of trust achieved in them. In the safety domain, explicit safety cases are increasingly required by law, regulations, and standards. In this article, we outline what a small, international group of experts, spanning various disciplines in safety, security, reliability, and critical infrastructure, been doing with the International Working Group on Assurance Cases (for Security), what we hope to achieve, and where we go next. 相似文献
199.
200.
Antoniades N. Boskovic A. Tomkos I. Madamopoulos N. Lee M. Roudas I. Pastel D. Sharma M. Yadlowsky M.J. 《Selected Areas in Communications, IEEE Journal on》2002,20(1):149-165
This paper demonstrates the use of computer simulation for topological design and performance engineering of transparent wavelength-division multiplexing metropolitan-area networks. Engineering of these networks involves the study of various transport-layer impairments such as amplifier noise, component ripple, chirp/dispersion, optical crosstalk, waveform distortion due to filter concatenation, fiber nonlinearities, and polarization effects. A computer simulation methodology composed of three main simulation steps is derived and implemented. This methodology obtains performance estimations by applying efficient wavelength-domain simulations on the entire network topology, followed by time-/frequency-domain simulations on selected paths of the network and finally Q-budgeting on an identified worst case path. The above technique provides an efficient tool for topological design and network performance engineering. Accurate simulation models are presented for each of the performance impairments, and the computer simulation methodology is used for the design and engineering of a number of actual metro network architectures 相似文献