全文获取类型
收费全文 | 27578篇 |
免费 | 1665篇 |
国内免费 | 75篇 |
专业分类
电工技术 | 384篇 |
综合类 | 40篇 |
化学工业 | 6276篇 |
金属工艺 | 1093篇 |
机械仪表 | 1669篇 |
建筑科学 | 547篇 |
矿业工程 | 8篇 |
能源动力 | 1074篇 |
轻工业 | 2518篇 |
水利工程 | 105篇 |
石油天然气 | 18篇 |
无线电 | 4641篇 |
一般工业技术 | 5918篇 |
冶金工业 | 1741篇 |
原子能技术 | 376篇 |
自动化技术 | 2910篇 |
出版年
2024年 | 34篇 |
2023年 | 353篇 |
2022年 | 536篇 |
2021年 | 907篇 |
2020年 | 645篇 |
2019年 | 678篇 |
2018年 | 916篇 |
2017年 | 889篇 |
2016年 | 1023篇 |
2015年 | 819篇 |
2014年 | 1256篇 |
2013年 | 1787篇 |
2012年 | 1889篇 |
2011年 | 2302篇 |
2010年 | 1706篇 |
2009年 | 1718篇 |
2008年 | 1530篇 |
2007年 | 1158篇 |
2006年 | 1034篇 |
2005年 | 901篇 |
2004年 | 812篇 |
2003年 | 740篇 |
2002年 | 715篇 |
2001年 | 592篇 |
2000年 | 513篇 |
1999年 | 494篇 |
1998年 | 782篇 |
1997年 | 481篇 |
1996年 | 447篇 |
1995年 | 303篇 |
1994年 | 200篇 |
1993年 | 167篇 |
1992年 | 136篇 |
1991年 | 112篇 |
1990年 | 90篇 |
1989年 | 98篇 |
1988年 | 83篇 |
1987年 | 70篇 |
1986年 | 57篇 |
1985年 | 47篇 |
1984年 | 39篇 |
1983年 | 29篇 |
1982年 | 31篇 |
1981年 | 28篇 |
1980年 | 32篇 |
1979年 | 14篇 |
1977年 | 22篇 |
1976年 | 34篇 |
1975年 | 18篇 |
1974年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Min-Seok Park Vladislav P. Vislovskiy Jong-San Chang Yong-Gun Shul Jin S. Yoo Sang-Eon Park 《Catalysis Today》2003,87(1-4):205-212
Alumina-supported vanadium oxide, VOx/Al2O3, and binary vanadium–antimony oxides, VSbOx/Al2O3, have been tested in the ethylbenzene dehydrogenation with carbon dioxide and characterized by SBET, X-ray diffraction, X-ray photoelectron spectroscopy, hydrogen temperature-programmed reduction and CO2 pulse methods. VSbOx/Al2O3 exhibited enhanced catalytic activity and especially on-stream stability compared to VOx/Al2O3 catalyst. Incorporation of antimony into VOx/Al2O3 increased dispersion of active VOx species, enhanced redox properties of the systems and formed a new mixed vanadium–antimony oxide phase in the most catalytically efficient V0.43Sb0.57Ox/Al2O3 system. 相似文献
62.
A new discontinuous modulation method based on space-vector control is proposed and analyzed. The proposed technique employs a pulse-dropping method and is designed in the time domain. It features a very wide modulation range while maintaining the required waveform qualities and switching numbers in the overmodulation region. Since the modulation method and modulation index equation are simple, the proposed technique can be easily implemented by software and is applicable to the overmodulation region in ac motor drives. The performance indexes are discussed and experiments have been performed. 相似文献
63.
Yan R.-H. Lee K.F. Jeon D.Y. Kim Y.O. Park B.G. Pinto M.R. Rafferty C.S. Tennant D.M. Westerwick E.H. Chin G.M. Morris M.D. Early K. Mulgrew P. Mansfield W.M. Watts R.K. Voshchenkov A.M. Bokor J. Swartz R.G. Ourmazd A. 《Electron Device Letters, IEEE》1992,13(5):256-258
The authors report the implementation of deep-submicrometer Si MOSFETs that at room temperature have a unity-current-gain cutoff frequency (f T) of 89 GHz, for a drain-to-source bias of 1.5 V, a gate-to-source bias of 1 V, a gate oxide thickness of 40 Å, and a channel length of 0.15 μm. The fabrication procedure is mostly conventional, except for the e-beam defined gates. The speed performance is achieved through an intrinsic transit time of only 1.8 ps across the active device region 相似文献
64.
Sang-Hoon Lee Dae Hwan Kim Kyung Rok Kim Jong Duk Lee Byung-Gook Park Young-Jin Gu Gi-Young Yang Jeong-Taek Kong 《Nanotechnology, IEEE Transactions on》2002,1(4):226-232
A practical model for a single-electron transistor (SET) was developed based on the physical phenomena in realistic Si SETs, and implemented into a conventional circuit simulator. In the proposed model, the SET current calculated by the analytic model is combined with the parasitic MOSFET characteristics, which have been observed in many recently reported SETs formed on Si nanostructures. The SPICE simulation results were compared with the measured characteristics of the Si SETs. In terms of the bias, temperature, and size dependence of the realistic SET characteristics, an extensive comparison leads to good agreement within a reasonable level of accuracy. This result is noticeable in that a single set of model parameters was used, while considering divergent physical phenomena such as the parasitic MOSFET, the Coulomb oscillation phase shift, and the tunneling resistance modulated by the gate bias. When compared to the measured data, the accuracy of the voltage transfer characteristics of a single-electron inverter obtained from the SPICE simulation was within 15%. This new SPICE model can be applied to estimating the realistic performance of a CMOS/SET hybrid circuit or various SET logic architectures. 相似文献
65.
66.
Joongsuk Park Cam Nguyen 《Microwave and Wireless Components Letters, IEEE》2002,12(6):221-222
A new compact millimeter-wave distance-measurement sensor prototype has been developed. The sensor is a step-frequency radar implemented using coherent heterodyne technique. It operates in Ka-band (26.5-40 GHz) and is realized using MICs and MMICs. The sensor transmits sinusoidal signals of incremental frequencies and demodulates the received signals into base-band I/Q signals for processing. Experimental results show that the sensor is capable of measuring distance with less than 0.2 inch of absolute error and a low transmitted power of only -20±3 dBm 相似文献
67.
A two-dimensional finite element model was constructed to analyze the simulated mechanical behavior of a cantilevered fixed partial denture. The variations of the models were made by altering the degree of bone support, the number of splinted abutments, and the length of the pontics. High stress concentrations were observed around the connectors of the fixed prosthesis and the tooth closest to the cantilever. Reduced bone support increased the deflection and stress concentrations. There was reduction in displacement and stress concentration when the teeth were splinted together. To improve the prognosis of the fixed partial denture cantilever, the number of abutments should be increased and the number of pontics decreased. 相似文献
68.
69.
Calculation of Mass Attenuation Coefficients of Beta Particles 总被引:1,自引:0,他引:1
Yi C.Y.; Han H.S.; Cho W.K.; Park U.J.; Jun J.S.; Chai H.S. 《Radiation protection dosimetry》1998,78(3):221-229
70.
Y. Ohshima H.S. Ahn M. Aoki S. Awa M. Fukushima H. Hayashii X.Q. Hu T.W. Hur S. Igarashi H. Ikeda H.C. Jeong K. Kaneyuki D.Y. Kim S.K. Kim A. Kuzmin M.H. Lee S. Noguchi A. Ochi H. Sagawa N. Sato N. Sugiyama K. Tamai T. Tanimori N. Toomi T.J. Wang K. Watanabe Y. Watanabe X.C. Zhong Y.C. Zhu 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1996,380(3):517-523
We studied the performance of a prototype electromagnetic calorimeter for the BELLE detector at the KEK proton synchrotron for an energy range of 0.25–3.5 GeV. The prototype consisted of an array of 6 × 5 CsI(Tl) crystals with 30 cm length (16.2 radiation lengths) and about 6 cm × 6 cm cross section. The scintillation light of each CsI(Tl) crystal was read out by two large-area PIN photodiodes and charge-sensitive preamplifiers attached at the rear face of the crystal. We measured the energy and position resolution for electrons and the e/π separation for two sets of matrix configurations: one corresponded to the center and the other to the edge of the barrel calorimeter. The overall performance measured by the test proves that the prototype calorimeter is satisfactory for the use in the BELLE detector. 相似文献