全文获取类型
收费全文 | 21810篇 |
免费 | 1453篇 |
国内免费 | 189篇 |
专业分类
电工技术 | 362篇 |
综合类 | 97篇 |
化学工业 | 5708篇 |
金属工艺 | 531篇 |
机械仪表 | 827篇 |
建筑科学 | 813篇 |
矿业工程 | 37篇 |
能源动力 | 1480篇 |
轻工业 | 2040篇 |
水利工程 | 350篇 |
石油天然气 | 337篇 |
武器工业 | 9篇 |
无线电 | 2252篇 |
一般工业技术 | 3910篇 |
冶金工业 | 680篇 |
原子能技术 | 157篇 |
自动化技术 | 3862篇 |
出版年
2024年 | 102篇 |
2023年 | 435篇 |
2022年 | 884篇 |
2021年 | 1406篇 |
2020年 | 1202篇 |
2019年 | 1392篇 |
2018年 | 1593篇 |
2017年 | 1444篇 |
2016年 | 1407篇 |
2015年 | 844篇 |
2014年 | 1350篇 |
2013年 | 2232篇 |
2012年 | 1443篇 |
2011年 | 1575篇 |
2010年 | 1069篇 |
2009年 | 946篇 |
2008年 | 641篇 |
2007年 | 516篇 |
2006年 | 439篇 |
2005年 | 290篇 |
2004年 | 264篇 |
2003年 | 210篇 |
2002年 | 174篇 |
2001年 | 117篇 |
2000年 | 111篇 |
1999年 | 102篇 |
1998年 | 159篇 |
1997年 | 133篇 |
1996年 | 121篇 |
1995年 | 90篇 |
1994年 | 62篇 |
1993年 | 75篇 |
1992年 | 57篇 |
1991年 | 54篇 |
1990年 | 56篇 |
1989年 | 44篇 |
1988年 | 31篇 |
1987年 | 30篇 |
1986年 | 41篇 |
1985年 | 33篇 |
1984年 | 41篇 |
1983年 | 35篇 |
1982年 | 25篇 |
1981年 | 21篇 |
1980年 | 21篇 |
1979年 | 22篇 |
1978年 | 21篇 |
1977年 | 20篇 |
1976年 | 25篇 |
1975年 | 13篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
22.
Xing Gu Shariar Sabuktagin Ali Teke Daniel Johnstone Hadis Morkoç Bill Nemeth Jeff Nause 《Journal of Materials Science: Materials in Electronics》2004,15(6):373-378
ZnO is a highly efficient photon emitter, and has optical and piezoelectric properties that are attractive for a variety of applications in sensors and potentially optoelectronic devices such as emitters. Due to its identical stacking order and close lattice match to GaN, it is also being developed as a substrate material for GaN epitaxy. However, the surface finish of the ZnO is such that much of the damage induced by sawing and follow up mechanical polishing remains. We developed a thermal treatment method to eliminate surface damage on the 0 face of ZnO (0 0 0 1) to prepare it for epitaxial growth. Atomic force microscopy images of ZnO (0 0 0 1) annealed at 1050 °C for 3 h etc. show that residual scratches from mechanical polishing are removed and atomically flat, terrace-like surfaces are attained. In addition, low-temperature photoluminescence and high-resolution X-ray diffraction measurements have been employed to investigate the effect of annealing on ZnO substrates. 相似文献
23.
Sheen D.M. Ali S.M. Oates D.E. Withers R.S. Kong J.A. 《Applied Superconductivity, IEEE Transactions on》1991,1(2):108-115
A method for the calculation of the current distribution, resistance, and inductance matrices for a system of coupled superconducting transmission lines having finite rectangular cross-section is presented. These calculations allow accurate characterization of both high-T c and low-T c superconducting strip transmission lines. For a single stripline geometry with finite ground planes, the current distribution, resistance, inductance, and kinetic inductance are calculated as functions of the penetration depth for various film thicknesses. These calculations are then used to determine the penetration depth for Nb, NbN, and YBa2Cu3O7-x superconducting thin films from the measured temperature dependence of the resonant frequency of a stripline resonator. The calculations are also used to convert measured temperature dependence of the quality factor to the intrinsic surface resistance as a function of temperature for an Nb stripline resonator 相似文献
24.
An analysis using maximum power-density criteria has been carried out for an endoreversible Carnot heat engine. The results have been compared with known results on maximum power analysis. The design parameters at maximum power density lead to smaller and more efficient endoreversible Carnot heat engines than those working at maximum power output. 相似文献
25.
26.
Ali Hassanzadeh 《Corrosion Science》2007,49(4):1895-1906
In our previous works, the corrosion inhibition properties of propylamine (PA), iso-propylamine (i-PA), butylamine (BA), tert-butylamine (t-BA), hexylamine (HA), ethylenediamine (EDA), diethanolamine (DEA), 3-amino-1-propanol (3-AP), 2-dimethylethanolamine (2-DEA), cyclohexylamine (CHA), N-methylcyclohexylamine (N-MCA) and dicyclohexylamine (DCHA) have been investigated by means of electrochemical impedance spectroscopy (EIS) with a carbon steel rotating disc electrode in some petroleum/water corrosive mixtures containing acetic acid and NaCl at 25 °C. In this work, the Kramers-Kronig transformations (KKTs) were applied to evaluate the validity of the impedance data of these amine compounds in hydrodynamic condition. The results obtained showed that experimental impedance data did not satisfy in K-K relations completely viz. indicated some errors. These errors were related to stray capacitances, external transmission line effects, pits formation and change in interface during data acquisition at high and low frequencies regions. In addition, the selection of a suitable equivalent circuit strongly emphasized to better interpret of EIS data which in turn cause better resulted KKTs spectra. With considering obtained transformations, more effective inhibitor was selected with regard to its charge transfer resistance, the corrosion capacitance and well satisfying in K-K relations. 相似文献
27.
Zhufang Liu Mohammad Shamsuzzoha Earl T. Ada W. Matthew Reichert David E. Nikles 《Journal of power sources》2007
Well-dispersed Pt nanoparticles with controlled size and narrow size distribution were prepared by polyalcohol reduction of platinum acetylacetonate, using oleylamine as a capping agent. The particle size was varied from 3.5 nm to 11.5 nm by decreasing the amount of oleylamine added in the synthesis. Size selection of the as-prepared particles by solvent fractionation yielded nearly monodispersed Pt particles. The as-prepared particles were loaded on a carbon support by physical deposition, but showed no electrocatalytic activity due to the oleylamine bound to the particle surface. The particles were activated for electrocatalysis after heating the particles in air at 185 °C for 5 h, conditions that gave no particle-sintering and no oxidation. Cyclic voltammetry showed that the particles after the heat treatment in air were electrocatalytically active for methanol oxidation. The smaller 3.5 nm and 4.0 nm Pt particles had a higher intrinsic activity for methanol oxidation, but a lower tolerance to CO poisoning, compared with 6.0 nm, 9.5 nm and 11.5 nm particles. CO-stripping results suggest that CO is more easily oxidized on larger Pt particles. 相似文献
28.
Koudymov A. Xuhong Hu Simin K. Simin G. Ali M. Yang J. Asif Khan M. 《Electron Device Letters, IEEE》2002,23(8):449-451
We demonstrate a novel RF switch based on a multifinger AlGaN/GaN MOSHFET. Record high saturation current and breakdown voltage, extremely low gate leakage current and low gate capacitance of the III-N MOSHFETs make them excellent active elements for RF switching. Using a single element test circuit with 1-mm wide multifinger MOSHFET we achieved 0.27 dB insertion loss and more than 40 dB isolation. These parameters can be further improved by impedance matching and by using submicron gate devices. The maximum switching power extrapolated from the results for 1A/mm 100 /spl mu/m wide device exceeds 40 W for a 1-mm wide 2-A/mm MOSHFET. 相似文献
29.
A Novel UWB Pulse Shape Modulation System 总被引:5,自引:1,他引:4
Ghavami Mohammad Michael Lachlan B. Haruyama Shinichiro Kohno Ryuji 《Wireless Personal Communications》2002,23(1):105-120
In this paper novel modified Hermite polynomial functions for use in impulse radio (ultra-wideband) communications are proposed. With these functions pulse shapes which are orthogonal and have nearly constant pulse width regardless of the pulse order are generated. These properties hold under the effects of differentiation. An M-ary communication system is constructed using these pulse shapes. A Matlab model for generating the pulses is designed and the effect of timing jitter on the performance of the system is investigated by computer simulation. 相似文献
30.
In this note we present a proof to the conjecture given in the above paper, and therefore establish the equivalence of characterizations of fixed modes for the general case. 相似文献