全文获取类型
收费全文 | 2409篇 |
免费 | 76篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 36篇 |
综合类 | 1篇 |
化学工业 | 707篇 |
金属工艺 | 52篇 |
机械仪表 | 40篇 |
建筑科学 | 87篇 |
矿业工程 | 2篇 |
能源动力 | 71篇 |
轻工业 | 186篇 |
水利工程 | 12篇 |
石油天然气 | 6篇 |
无线电 | 288篇 |
一般工业技术 | 418篇 |
冶金工业 | 280篇 |
原子能技术 | 20篇 |
自动化技术 | 280篇 |
出版年
2022年 | 13篇 |
2021年 | 48篇 |
2020年 | 13篇 |
2019年 | 22篇 |
2018年 | 35篇 |
2017年 | 38篇 |
2016年 | 48篇 |
2015年 | 22篇 |
2014年 | 57篇 |
2013年 | 118篇 |
2012年 | 91篇 |
2011年 | 116篇 |
2010年 | 93篇 |
2009年 | 106篇 |
2008年 | 106篇 |
2007年 | 107篇 |
2006年 | 91篇 |
2005年 | 77篇 |
2004年 | 66篇 |
2003年 | 67篇 |
2002年 | 86篇 |
2001年 | 43篇 |
2000年 | 43篇 |
1999年 | 51篇 |
1998年 | 82篇 |
1997年 | 66篇 |
1996年 | 58篇 |
1995年 | 47篇 |
1994年 | 37篇 |
1993年 | 38篇 |
1992年 | 33篇 |
1991年 | 36篇 |
1990年 | 37篇 |
1989年 | 31篇 |
1988年 | 27篇 |
1987年 | 32篇 |
1986年 | 27篇 |
1985年 | 45篇 |
1984年 | 37篇 |
1983年 | 20篇 |
1982年 | 27篇 |
1981年 | 20篇 |
1980年 | 18篇 |
1979年 | 33篇 |
1978年 | 23篇 |
1977年 | 25篇 |
1976年 | 25篇 |
1975年 | 24篇 |
1974年 | 15篇 |
1973年 | 19篇 |
排序方式: 共有2486条查询结果,搜索用时 15 毫秒
1.
2.
Ting Gang Zhu Uttiya Chowdhury Michael M. Wong Jonathan C. Denyszyn Russell D. Dupuis 《Journal of Electronic Materials》2002,31(5):406-410
In this paper, we report the study of the electrical characteristics of GaN and AlGaN vertical p-i-n junctions and Schottky
rectifiers grown on both sapphire and SiC substrates by metal-organic chemical-vapor deposition. For GaN p-i-n rectifiers
grown on SiC with a relatively thin “i” region of 2 μm, a breakdown voltage over 400 V, and forward voltage as low as 4.5
V at 100 A/cm2 are exhibited for a 60-μm-diameter device. A GaN Schottky diode with a 2-μm-thick undoped layer exhibits a blocking voltage
in excess of ∼230 V at a reverse-leakage current density below 1 mA/cm2, and a forward-voltage drop of 3.5 V at a current density of 100 A/cm2. It has been found that with the same device structure and process approach, the leakage current of a device grown on a SiC
substrate is much lower than a device grown on a sapphire substrate. The use of Mg ion implantation for p-guard rings as planar-edge
terminations in mesageometry GaN Schottky rectifiers has also been studied. 相似文献
3.
Wong M.M. Chowdhury U. Sicault D. Becher D.T. Denyszyn J.C. Zhu T.G. Feng M. Dupuis R.D. 《Electronics letters》2002,38(9):428-429
The performance of an innovative delta-doped AlGaN/AlN/GaN heterojunction field-effect transistor (HFET) structure is reported. The epitaxial heterostructures were grown on semi-insulating SiC substrates by low-pressure metalorganic chemical vapour deposition. These structures exhibit a maximum carrier mobility of 1058 cm2/V s and a sheet carrier density of 2.35×1013 cm-2 at room temperature, corresponding to a large ns μn product of 2.49×1016 V s. HFET devices with 0.25 μm gate length were fabricated and exhibited a maximum current density as high as 1.5 A/mm (at VG=+1 V) and a peak transconductance of gm=240 mS/mm. High-frequency device measurements yielded a cutoff frequency of ft≃50 GHz and maximum oscillation frequency fmax≃130 GHz 相似文献
4.
The extinction coefficient ? at 2.9 μm for OH in fluoride glasses is measured by determining the amount of HF evolved during heating of the glass under steam and the corresponding intensity of the OH absorption band. This coefficient is respectively equal to 31 litre mole?1 cm?1 for BTYbZ glass (15 BaF2 - 29 ThF4 - 28 YbF3 - 28 ZnF2) and 19.5 litre mole?1 cm?1 for BALLA glass (34 BaF2 - 57 ZrF4 - 4 AlF3 - 5 LaF3). 相似文献
5.
An assessment of the Fe-C-Si system 总被引:1,自引:0,他引:1
6.
Andr Hamwi Catherine Latouche B atrice Burteaux Jacques Dupuis 《Fullerenes, Nanotubes and Carbon Nanostructures》1996,4(6):1213-1226
Reaction of metallic fluorides: WF6 TaF5, NbF5 and TiF4 with C60/C70 extract was performed at appropriate temperatures. M0F5 and BF3 fluorides do not react. Chemical formulas based on mass uptake show MFn/C60 ratios up to 2.00. Compounds were analysed by means of X-ray diffraction, FT-IR and NMR spectroscopies. The presence of neutral fluorides and associated anionic species is put forward and it is shown that MFn compounds do not act as fluorination agents. Electrical conductivity measurements are also presented. 相似文献
7.
Data transmission networks and systems are often subject to perturbations due to the fact that (low level) data signals are surrounded by perturbing electromagnetic fields. This paper presents and analyses information perturbing mechanisms. The authors examine data streams transmitted by an elementary system which represents the basis of any electronic device. We show the influence of technological families of cmos circuits and present a test method and bench to investigate the sensitivity of devices under test by means of statistical parameters. 相似文献
8.
Tony Maillet Jacques Barbier Jr. Daniel Duprez 《Applied catalysis. B, Environmental》1996,9(1-4):251-266
A 1% Pd catalyst (38% dispersion) was prepared by impregnating a γ-alumina with palladium acetylacetonate dissolved in acetone. The behaviour of this catalyst in oxidation and steam reforming (SR) of propane was investigated. Temperature-programmed reactions of C3H8 with O2 or with O2 + H2O were carried out with different stoichiometric ratios S(S =[O2]/5[C3H8]). The conversion profiles of C3H8 for the reaction carried out in substoichiometry of O2 (S < 1) showed two discrete domains of conversion: oxidation at temperatures below 350°C and SR at temperatures above 350°C. The presence of steam in the inlet gases is not necessary for SR to occur: there is sufficient water produced in the oxidation to form H2 and carbon oxides by this reaction. Contrary to what was observed with Pt, an apparent deactivation between 310 and 385°C could be observed with Pd in oxidation. This is due to a reduction of PdOx into Pd0, which is much less active than the oxide in propane oxidation. Steam added to the reactants inhibits oxidation while it prevents the reduction of PdOx into Pd0. Compared to Pt and to Rh, Pd has a higher thermal resistance: no deactivation occurred after treatment up to 700°C and limited deactivation after treatment up to 900°C, provided that the catalyst is maintained in an oxygen-rich atmosphere during the cooling. 相似文献
9.
10.
Fatima Bennour Jacques Rogez Jean Claude Mathieu 《Journal of the American Ceramic Society》1996,79(10):2752-2754
The Na2 O-Cs2O-SiO2 system has been investigated by means of a new differential thermal analysis apparatus. Two compounds have been observed for the first time in the metasilicate and disilicate joins. The CsNaSi2 O5 disilicate melts congruently at 1217 K and the peritectic fusion of the CsNaSiO3 metasilicate occurs at 1120 K. 相似文献