全文获取类型
收费全文 | 500004篇 |
免费 | 5980篇 |
国内免费 | 1457篇 |
专业分类
电工技术 | 9210篇 |
综合类 | 480篇 |
化学工业 | 75719篇 |
金属工艺 | 20165篇 |
机械仪表 | 15329篇 |
建筑科学 | 12007篇 |
矿业工程 | 2710篇 |
能源动力 | 12070篇 |
轻工业 | 44082篇 |
水利工程 | 5240篇 |
石油天然气 | 9966篇 |
武器工业 | 83篇 |
无线电 | 59392篇 |
一般工业技术 | 97014篇 |
冶金工业 | 90852篇 |
原子能技术 | 11488篇 |
自动化技术 | 41634篇 |
出版年
2021年 | 3782篇 |
2019年 | 3646篇 |
2018年 | 6448篇 |
2017年 | 6459篇 |
2016年 | 6887篇 |
2015年 | 4423篇 |
2014年 | 7519篇 |
2013年 | 21448篇 |
2012年 | 12093篇 |
2011年 | 16438篇 |
2010年 | 13254篇 |
2009年 | 14999篇 |
2008年 | 15890篇 |
2007年 | 15723篇 |
2006年 | 14160篇 |
2005年 | 13090篇 |
2004年 | 12375篇 |
2003年 | 12064篇 |
2002年 | 11887篇 |
2001年 | 11746篇 |
2000年 | 11198篇 |
1999年 | 11327篇 |
1998年 | 26618篇 |
1997年 | 19460篇 |
1996年 | 15349篇 |
1995年 | 11822篇 |
1994年 | 10628篇 |
1993年 | 10451篇 |
1992年 | 8223篇 |
1991年 | 7830篇 |
1990年 | 7519篇 |
1989年 | 7399篇 |
1988年 | 7215篇 |
1987年 | 6215篇 |
1986年 | 6130篇 |
1985年 | 7161篇 |
1984年 | 6766篇 |
1983年 | 6114篇 |
1982年 | 5779篇 |
1981年 | 6013篇 |
1980年 | 5713篇 |
1979年 | 5486篇 |
1978年 | 5444篇 |
1977年 | 6308篇 |
1976年 | 7995篇 |
1975年 | 5008篇 |
1974年 | 4850篇 |
1973年 | 4889篇 |
1972年 | 4094篇 |
1971年 | 3846篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
Experimental and numerical assessment of gate-lag phenomena in AlGaAs-GaAs heterostructure field-effect transistors (FETs) 总被引:1,自引:0,他引:1
Verzellesi G. Mazzanti A. Basile A.F. Boni A. Zanoni E. Canali C. 《Electron Devices, IEEE Transactions on》2003,50(8):1733-1740
Gate-lag effects are characterized in AlGaAs-GaAs heterostructure field-effect transistors (HFETs) by means of measurements and numerical device simulations. Gate lag increasingly affects device switching at increasing ungated recess extension, suggesting that responsible deep levels be located at the ungated, recess surface of the HFET. Gate lag diminishes by making the off-state gate-source voltage less negative and by increasing the drain bias. Increasing the temperature makes the turn-on transient faster at low drain bias, while slightly delaying it at high drain bias. Numerical device simulations accounting for acceptor-like traps at the ungated surface predict gate-lag phenomena in good agreement with experiments, reproducing correctly the observed bias and temperature dependences. Simulations show that surface states behave, during the turn-on transient, as hole traps capturing holes attracted at the ungated surface by the negative trapped charge. 相似文献
103.
B. Pantchev P. Danesh K. Antonova B. Schmidt D. Grambole J. Baran 《Journal of Materials Science: Materials in Electronics》2003,14(10-12):751-752
The hydrogen content, its depth distribution, and its bonding configuration have been studied in hydrogenated amorphous silicon prepared by plasma-enhanced chemical vapor deposition with hydrogen-diluted silane. Nuclear reaction analysis and infrared spectroscopy were used to determine the total amount of hydrogen and its bonded component, respectively. It has been established that the total concentration of hydrogen does not depend on the film thickness, and has a uniform depth profile. The concentration of bonded hydrogen changes with the film thickness within the measurement accuracy. The data obtained suggest the presence of molecular (non-bonded) hydrogen, uniformly distributed in concentration across the film thickness. 相似文献
104.
Hook T.B. Brown J. Cottrell P. Adler E. Hoyniak D. Johnson J. Mann R. 《Electron Devices, IEEE Transactions on》2003,50(9):1946-1951
Lateral scattering of retrograde well implants is shown to have an effect on the threshold voltage of nearby devices. The threshold voltage of both NMOSFETs and PMOSFETs increases in magnitude for conventional retrograde wells, but for triple-well isolated NMOSFETs the threshold voltage decreases for narrow devices near the edge of the well. Electrical data, SIMS, and SUPREM4 simulations are shown that elucidate the phenomenon. 相似文献
105.
We report for the first time optical signal-to-noise penalties which lead to performance degradations in single-fiber long-reach optical access networks when compared to identical dual-fiber systems. A simplified architecture, with reduced optical amplifier count compared to previous work, for single-fiber operation of a symmetrical 10-Gb/s, 1024-way split, 110-km long-reach optical access network is presented and demonstrated. In addition, a possible solution to remove the optical signal-to-noise penalty is suggested 相似文献
106.
The strong tendency of organic nanoparticles to rapidly self‐assemble into highly aligned superlattices at room temperature when solution‐cast from dispersions or spray‐coated directly onto various substrates is described. The nanoparticle dispersions are stable for years. The novel precipitation process used is believed to result in molecular distances and alignments in the nanoparticles that are not normally possible. Functional organic light‐emitting diodes (OLEDs)—which have the same host–dopant emissive‐material composition—with process‐tunable electroluminescence have been built with these nanoparticles, indicating the presence of novel nanostructures. For example, only changing the conditions of the precipitation process changes the OLED emission from green light to yellow. 相似文献
107.
An increase in hydrogen evolution from the hydrogen-evolving enzyme in the actinomycete Frankia was recorded in the presence of nickel. Immunogold localisation analysis of the intracellular distribution of hydrogenase proteins indicated that they were evenly distributed in the membranes and cytosol of both hyphae and vesicles. In addition, molecular characterisation of the hydrogen-evolving enzyme at the proteomic level, using two-dimensional gel electrophoresis combined with mass spectrometry, confirmed that the Frankia hydrogen-evolving enzyme is similar to the cyanobacterial bidirectional hydrogenase of Anabena siamensis. 相似文献
108.
Bart J Kemps Flip R Bamelis Bart De Ketelaere Kristof Mertens Kokou Tona Eddy M Decuypere Josse G De Baerdemaeker 《Journal of the science of food and agriculture》2006,86(9):1399-1406
The objective of this research was to investigate the feasibility of visible transmission spectroscopy for the non‐destructive assessment of the freshness of an individual egg. A total of 600 intact white‐shelled eggs of the same flock (Lohmann, 40 weeks of age) were measured. To obtain a considerable variation in freshness, groups consisting of 60 eggs were stored (18 °C, 55% RH) for 0, 2, 4, 6, 8, 10, 12, 14, 16 and 18 days. The non‐destructive spectral measurements were compared with the two most widely used destructive freshness parameters, namely Haugh units and albumen pH. A partial least squares (PLS1) model was built in order to predict Haugh units and pH of the albumen based on the transmission spectra. The correlation coefficients between the predicted value and the measured value were 0.842 and 0.867 for Haugh unit and pH of the albumen, respectively. These results show that the light transmission spectrum of an egg provides quantitative information about egg freshness. Relevant information concerning egg freshness is restricted to the interval between 570 and 750 nm. Furthermore, the models obtained for both destructive parameters were strikingly similar, indicating that Haugh unit and pH have the same physico‐chemical background. Copyright © 2006 Society of Chemical Industry 相似文献
109.
110.