全文获取类型
收费全文 | 749774篇 |
免费 | 8460篇 |
国内免费 | 1682篇 |
专业分类
电工技术 | 13672篇 |
综合类 | 602篇 |
化学工业 | 118234篇 |
金属工艺 | 30627篇 |
机械仪表 | 23443篇 |
建筑科学 | 17501篇 |
矿业工程 | 5252篇 |
能源动力 | 19173篇 |
轻工业 | 62472篇 |
水利工程 | 8738篇 |
石油天然气 | 18161篇 |
武器工业 | 48篇 |
无线电 | 80488篇 |
一般工业技术 | 151097篇 |
冶金工业 | 130735篇 |
原子能技术 | 18223篇 |
自动化技术 | 61450篇 |
出版年
2021年 | 6699篇 |
2019年 | 6360篇 |
2018年 | 11153篇 |
2017年 | 11258篇 |
2016年 | 11901篇 |
2015年 | 7539篇 |
2014年 | 12701篇 |
2013年 | 34139篇 |
2012年 | 19770篇 |
2011年 | 26675篇 |
2010年 | 21568篇 |
2009年 | 24063篇 |
2008年 | 24543篇 |
2007年 | 24161篇 |
2006年 | 21043篇 |
2005年 | 19297篇 |
2004年 | 18285篇 |
2003年 | 17842篇 |
2002年 | 17447篇 |
2001年 | 16976篇 |
2000年 | 16229篇 |
1999年 | 16106篇 |
1998年 | 37785篇 |
1997年 | 27600篇 |
1996年 | 21481篇 |
1995年 | 16497篇 |
1994年 | 14922篇 |
1993年 | 14555篇 |
1992年 | 11246篇 |
1991年 | 10973篇 |
1990年 | 10780篇 |
1989年 | 10577篇 |
1988年 | 10167篇 |
1987年 | 9071篇 |
1986年 | 8851篇 |
1985年 | 10132篇 |
1984年 | 9355篇 |
1983年 | 8898篇 |
1982年 | 8031篇 |
1981年 | 8277篇 |
1980年 | 7866篇 |
1979年 | 7925篇 |
1978年 | 7816篇 |
1977年 | 8866篇 |
1976年 | 11241篇 |
1975年 | 7080篇 |
1974年 | 6789篇 |
1973年 | 6876篇 |
1972年 | 5902篇 |
1971年 | 5523篇 |
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
81.
We predict that, for wavelength division multiplexing optical-network applications, an asymmetrically dilated configuration of a 2×2 cross-connect is significantly better in terms of overall crosstalk when the levels of the bar-port crosstalk and the cross-port crosstalk are significantly different from each other, as is the case with optical-frequency filters which utilize grating-assisted coupling. As a verification, we present a simulation study with 2×2 polarization-diversified acousto-optic tunable filters. We present a recursive method to extend the principle of asymmetric dilation to larger-size cross-connect switches, and make a recommendation for an asymmetrically dilated 4×4 cross-connect configuration 相似文献
82.
Neviani A. Meneghesso G. Zanoni E. Hafizi M. Canali C. 《Electron Device Letters, IEEE》1997,18(12):619-621
Impact ionization is a major limiting factor to the maximum operating voltage of InGaAs-based, high-speed transistors. In this work, data on the positive temperature dependence of the electron impact ionization coefficient αn in In0.53Ga0.47As at medium-low electric fields are reported for the first time. The increase of αn with temperature is opposite to the behavior normally observed in most semiconductors. This anomalous behavior implies the onset of a positive feedback between power dissipation and avalanche generation which may adversely affect the power handling capability of In0.53Ga 0.47As-based devices, and which should be taken into account in device thermal modeling. In the experimental procedure, based on the measurement of the multiplication factor M-1 in npn In0.53Ga 0.47As/InP Heterojunction Bipolar Transistors (HBT), particular care has been taken in order to rule out possible spurious, temperature-dependent contributions to the measured multiplication current 相似文献
83.
84.
Fahmy H.I. Develekos G. Douligeris C. 《Selected Areas in Communications, IEEE Journal on》1997,15(2):226-237
Communication network design is becoming increasingly complex, involving making networks more usable, affordable, and reliable. To help with this, we have proposed an expert network designer (END) for configuring, modeling, simulating, and evaluating large structured computer networks, employing artificial intelligence, knowledge representation, and network simulation tools. We present a neural network/knowledge acquisition machine-learning approach to improve the END's efficiency in solving the network design problem and to extend its scope to acquire new networking technologies, learn new network design techniques, and update the specifications of existing technologies 相似文献
85.
Single-phase voltage source power converters (VSCs) under consideration are AC-DC current-controlled boost-type power converters with bidirectional power-handling capability. Equivalence between two series-connected two-level power converters and a single three-level power converter is considered here. Further considered is the series operation of three-level power converters. Simulation results and experimental verification for both are provided. Economical configurations of three-level power converters leading to multilevel waveforms are presented thereafter 相似文献
86.
Cresswell M.W. Allen R.A. Guthrie W.F. Sniegowski J.J. Ghoshtagore R.N. Linholm L.W. 《Semiconductor Manufacturing, IEEE Transactions on》1998,11(2):182-193
The physical widths of reference features incorporated into electrical linewidth test structures patterned in films of monocrystalline silicon have been determined from Kelvin voltage measurements. The films in which the test structures are patterned are electrically insulated from the bulk-silicon substrate by a layer of silicon dioxide provided by SIMOX (Separation by the IMplantation of OXygen) processing. The motivation is to facilitate the development of linewidth reference materials for critical-dimension (CD) metrology-instrument calibration. The selection of the (110) orientation of the starting silicon and the orientation of the structures' features relative to the crystal lattice enable a lattice-plane-selective etch to generate reference-feature properties of rectangular cross section and atomically planar sidewalls. These properties are highly desirable for CD applications in which feature widths are certified with nanometer-level uncertainty for use by a diverse range of CD instruments. End applications include the development and calibration of new generations of CD instruments directed at controlling processes for manufacturing devices having sub-quarter-micrometer features 相似文献
87.
A new commercially available diode model is described. This unified model is capable of simulating the widest range of diode technologies of any presently available. The emphasis of this paper is on describing the model's extensive features and flexibility in the different domains of operation and is of particular interest in power applications 相似文献
88.
For part I see, ibid., p. 134, 1998. The basic approach outlined in the previous article is applied to the difficult problem of computing the optical modes of a vertical-cavity surface-emitting laser. The formulation utilizes a finite difference equation based upon the lowest order term of an infinite series solution of the scalar Helmholtz equation in a local region. This difference equation becomes exact in the one-dimensional (1-D) limit, and is thus ideally suited for nearly 1-D devices such as vertical-cavity lasers. The performance of the resulting code is tested on both a simple cylindrical cavity with known solutions and an oxide-confined vertical-cavity laser structure, and the results compared against second-order-accurate code based upon Crank-Nicolson differencing 相似文献
89.
The capacitive idling converters derived from the Cuk, SEPIC, Zeta, and flyback topologies allow soft commutation of power switches without the need for additional circuitry, making it possible to increase the switching frequency while maintaining high efficiency 相似文献
90.
Pipelining and bypassing in a VLIW processor 总被引:1,自引:0,他引:1
This short note describes issues involved in the bypassing mechanism for a very long instruction word (VLIW) processor and its relation to the pipeline structure of the processor. The authors first describe the pipeline structure of their processor and analyze its performance and compare it to typical RISC-style pipeline structures given the context of a processor with multiple functional units. Next they study the performance effects of various bypassing schemes in terms of their effectiveness in resolving pipeline data hazards and their effect on the processor cycle time 相似文献