全文获取类型
收费全文 | 1029013篇 |
免费 | 61562篇 |
国内免费 | 39292篇 |
专业分类
电工技术 | 53827篇 |
综合类 | 50674篇 |
化学工业 | 138130篇 |
金属工艺 | 57757篇 |
机械仪表 | 51533篇 |
建筑科学 | 47903篇 |
矿业工程 | 23033篇 |
能源动力 | 26559篇 |
轻工业 | 98321篇 |
水利工程 | 22653篇 |
石油天然气 | 26270篇 |
武器工业 | 7140篇 |
无线电 | 110922篇 |
一般工业技术 | 151908篇 |
冶金工业 | 126078篇 |
原子能技术 | 18568篇 |
自动化技术 | 118591篇 |
出版年
2023年 | 8208篇 |
2022年 | 20333篇 |
2021年 | 27634篇 |
2020年 | 19834篇 |
2019年 | 15813篇 |
2018年 | 25785篇 |
2017年 | 27704篇 |
2016年 | 23677篇 |
2015年 | 26135篇 |
2014年 | 34952篇 |
2013年 | 54353篇 |
2012年 | 54975篇 |
2011年 | 66631篇 |
2010年 | 60177篇 |
2009年 | 59534篇 |
2008年 | 60980篇 |
2007年 | 61300篇 |
2006年 | 46736篇 |
2005年 | 42086篇 |
2004年 | 33236篇 |
2003年 | 26469篇 |
2002年 | 24112篇 |
2001年 | 22817篇 |
2000年 | 19958篇 |
1999年 | 15456篇 |
1998年 | 33580篇 |
1997年 | 23493篇 |
1996年 | 17897篇 |
1995年 | 13423篇 |
1994年 | 11585篇 |
1993年 | 11270篇 |
1992年 | 8124篇 |
1991年 | 7633篇 |
1990年 | 7453篇 |
1989年 | 7189篇 |
1988年 | 6576篇 |
1987年 | 5855篇 |
1986年 | 5753篇 |
1985年 | 6253篇 |
1984年 | 5873篇 |
1983年 | 5153篇 |
1982年 | 4857篇 |
1981年 | 4998篇 |
1980年 | 4782篇 |
1979年 | 4625篇 |
1978年 | 4360篇 |
1977年 | 5317篇 |
1976年 | 6985篇 |
1975年 | 3747篇 |
1973年 | 3631篇 |
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
991.
The high-frequency internal impedance model of a round ohmic conductor is incorporated into the subcell thin-wire formulation of the finite-difference time-domain method to model the microwave properties of metal wires. For magnetic metals, such as steel, an effective conductivity is introduced to account for the increase in ohmic loss due to the high-frequency permeability. Physical experiments with half-wave resonant copper- and steel-wire inclusions, supported by a dielectric slab in a standard S-band rectangular waveguide, support the formulation 相似文献
992.
This paper proposes a method to reduce the vibration of the three-phase HB-type stepping motor with cogging torque by the feedforward compensation control. The compensation signal to suppress the vibration of the motor frame is obtained by the repetitive controller installing an online Fourier transformer and utilizing an acceleration sensor attached to the motor frame or an acoustic sensor such as a microphone placed close to the frame. The sensor is used only for the acquisition of the feedforward compensation data. The feedforward compensation signal at an arbitrary operating point is derived from the amplitude and phase data of the frequency components and the operating point data. Compensation data obtained by the repetitive controller is applied to the operating point changed by reference frequency and load condition in steady state. The compensation signal for the new operating point will be generated from compensation data utilizing polynomial equation approximation and linear interpolation method. The effectiveness of this proposed method is confirmed by the experimental results. 相似文献
993.
PMN-PT陶瓷中的氧缺位及其消除 总被引:1,自引:0,他引:1
研究了组成中Pb含量的变化对组成为Pbx(Mg1/3Nb2/3)0.65Ti0.35O3的铌镁酸铅-钛酸铅(PMN-PT)陶瓷压电性能的影响,发现化学计量比组成(x=1)的Pbx(Mg1/3Nb2/3)0.65Ti0.35O3陶瓷经常出现压电性能的大幅度退化现象,而A位适量缺Pb能稳定地获得高性能的Pbx(Mg1/3Nb2/3)0.65Ti0.35O3陶瓷。XPS元素价态分析的结果表明,化学计量比的Pbx(Mg1/3Nb2/3)0.65Ti0.35O3陶瓷中含有较多的氧缺位,氧缺位的产生源于MgNb2O6(MN)合成过程中的气氛差异,A位适量缺Pb能有效地消除这种氧缺位而稳定地获得正常的压电性能,其机理被认为是氧缺位与铅缺位的复合。 相似文献
994.
A new hybrid automatic repeat request scheme employing packet combining based on the Viterbi decoder is presented. It is shown that the proposed form of combining, together with a rearrangement of the signal constellation, can outperform similar forms of packet combining such as average diversity combining 相似文献
995.
Yoshitomi T. Saito M. Ohguro T. One M. Momose H.S. Morifuji E. Morimoto T. Katsumata Y. Iwai H. 《Electron Devices, IEEE Transactions on》1998,45(6):1295-1299
A silicided silicon-sidewall source and drain (S4D) structure is proposed for sub-0.1-μm devices. The merit of the S4D structure is that the series resistance of the source and drain is significantly reduced since the silicide layer is attached very close to the gate electrode and the silicon sidewall can be doped very highly. Thus, very high drain current drive can be expected, Another advantage of this structure is that the source and drain extensions are produced by the solid-phase diffusion of boron from the highly doped silicon-sidewall. Thus, shallow extensions with very high doping can be realized. A 75-nm gate length pMOSFET fabricated with this structure is shown to exhibit excellent electrical characteristics 相似文献
996.
A modification to the `shape-invariant' sinusoidal speech model is proposed, whereby the phases of the component sinewaves used for the excitation are made to add coherently at each glottal closure. Applied to pitch and time-scale modification, higher quality synthetic speech is produced when large changes are required 相似文献
997.
Parametric DC measurements on pseudomorphic AlGaAs/InGaAs modulation-doped field-effect transistors (MODFETs) were carried out over the 300-405 K temperature range. A gradual channel device model was developed to simulate the temperature dependent behavior and assist in the interpretation of the characteristics. The simulations are shown to provide good predictive ability and confirm the physical reasons why the zero temperature coefficient point of a MODFET occurs only for gate bias voltages below the threshold voltage 相似文献
998.
Andoh E. Kosugi M. Kawamura T. Araki S. Taketoshi K. 《Electron Devices, IEEE Transactions on》1998,45(4):778-784
We developed a novel image intensifier (II) of an amplified metal-oxide-semiconductor (MOS) imager (AMI) overlaid with electron-bombarded (EB) amorphous silicon (a-Si). The electron bombardment gain (EB gain) was 1500 at an accelerating voltage of 10 kV. Since the multiplication process was free from a phosphorescent screen and a coupling fiber plate as in the conventional II, the resolution was high and the picture quality was good and free from granularity noises, white spots, lag and sticking. As for fatigue of X-ray irradiation, the contrasts of a vertical stripe (Smear) are not detectable and damaged areas in AMI are weak whereas both of those in charge-coupled devices (CCDs) are strong 相似文献
999.
Presents the Satellite Communications Network Expert (SaNE), a knowledge-based aid designed to provide engineering support for fault diagnosis. The SaNE is composed of two elements: a satcom network model, which simulates the structure and functionality of a system based loosely upon a large military satcom network, and a diagnostic component, which uses knowledge- and model-based reasoning techniques to analyse system anomalies and diagnose possible causes for the alarms such networks generate. The development cycle is described, emphasising lessons learnt during development and testing and the advantages and disadvantages of the techniques applied. The goal of the SaNE project is primarily commercial acceptance rather than innovation. The authors illustrate how novel concepts can be implemented in a practical system without compromising this goal 相似文献
1000.