全文获取类型
收费全文 | 1672篇 |
免费 | 184篇 |
国内免费 | 480篇 |
专业分类
电工技术 | 62篇 |
综合类 | 51篇 |
化学工业 | 67篇 |
金属工艺 | 53篇 |
机械仪表 | 22篇 |
矿业工程 | 3篇 |
能源动力 | 19篇 |
轻工业 | 2篇 |
石油天然气 | 2篇 |
武器工业 | 1篇 |
无线电 | 1575篇 |
一般工业技术 | 365篇 |
冶金工业 | 17篇 |
原子能技术 | 33篇 |
自动化技术 | 64篇 |
出版年
2024年 | 1篇 |
2023年 | 17篇 |
2022年 | 30篇 |
2021年 | 54篇 |
2020年 | 46篇 |
2019年 | 52篇 |
2018年 | 27篇 |
2017年 | 63篇 |
2016年 | 78篇 |
2015年 | 79篇 |
2014年 | 93篇 |
2013年 | 85篇 |
2012年 | 101篇 |
2011年 | 192篇 |
2010年 | 119篇 |
2009年 | 165篇 |
2008年 | 147篇 |
2007年 | 160篇 |
2006年 | 156篇 |
2005年 | 107篇 |
2004年 | 105篇 |
2003年 | 87篇 |
2002年 | 72篇 |
2001年 | 65篇 |
2000年 | 57篇 |
1999年 | 44篇 |
1998年 | 39篇 |
1997年 | 56篇 |
1996年 | 19篇 |
1995年 | 15篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1989年 | 1篇 |
排序方式: 共有2336条查询结果,搜索用时 46 毫秒
91.
An analytical model of Al0.15Ga0.85N/GaN modulation doped field effect transistor (MODFET), which uses an accurate velocity field relationship and incorporates the dominant effect of piezoelectric polarization induced charge at the AlGaN/GaN interface is presented. The effect of traps has also been taken into account. The calculated DC characteristics are in excellent agreement with the measured data. The model is extended to predict the microwave performance of the device. High current levels (>500 mA/mm), large transconductance (160.83 mS/mm) and a high cutoff frequency (9.6 GHz) have been achieved analytically and are in close agreement with the experimental data. 相似文献
92.
In this work, we focus on the fabrication of cubic GaN based Schottky-barrier devices (SBDs) and measured current voltage (I-V) characteristics and the critical field for electronic breakdown. Phase-pure cubic GaN and c-AlxGa1 − xN/GaN structures were grown by plasma assisted molecular beam epitaxy (MBE) on 200 μm thick free-standing 3C-SiC (1 0 0) substrates, which were produced by HOYA Advanced Semiconductor Technologies Co., Ltd. The thickness of the c-GaN and c-Al0.3Ga0.7N epilayers were about 600 and 30 nm, respectively. Ni/In Schottky contacts 300 μm in diameter were produced on c-GaN and c-Al0.3Ga0.7N/GaN structures by thermal evaporation using contact lithography. A clear rectifying behavior was measured in our SBDs and the I-V behavior was analyzed in detail, indicating the formation of a thin surface barrier at the Ni-GaN interface. Annealing of the Ni Schottky contacts in air at 200 °C reduces the leakage current by three orders of magnitude. The doping density dependence of breakdown voltages derived from the reverse breakdown voltage characteristics of c-GaN SBDs is investigated. The experimental values of breakdown voltage in c-GaN are in good agreement with theoretical values and show the same dependence on doping level as in hexagonal GaN. From our experimental data, we extrapolate a blocking voltage of 600 V in c-GaN films with a doping level ND = 5 × 1015 cm−3. 相似文献
93.
D. E. Walker Jr. M. Gao X. Chen W. J. Schaff L. J. Brillson 《Journal of Electronic Materials》2006,35(4):581-586
A new approach to studying Schottky barrier formation on a nanometer scale is demonstrated using both Auger electron spectroscopy
core level shift and secondary electron threshold work function measurements on cleaved epilayers. Band bending induced by
metallization of cleaved epilayer surfaces can be investigated without introducing defects due to chemical or ion beam surface
cleaning. For GaN epilayers, this approach also avoids complications due to piezoelectric effects on polar-axis growth surfaces.
Initial investigations of Au and Ag Schottky contact formation on GaN in ultrahigh vacuum reveal the presence of a pinning
level ∼1.7 eV above the valence band edge. 相似文献
94.
We report on the details of controlled fabrication of highly crystalline gallium nitride (GaN) two-dimensional highly periodic
ultradense nanopore and nanopillar arrays by self-assembly nanopatterning. Nanopore synthesis relies on the use of anodized
alumina oxide template as a mask for dry etching of GaN top surface using chlorine gas. The inverse patterning is accomplished
by site-selective deposition of metal nanodot array by e-beam evaporation of Ni through the pores of the template; after which
the template is removed and dry etching is performed. The formed patterns demonstrate an excellent hexagonal order and uniformity
according to fast Fourier transformation performed. The presented approach is robust, highly reproducible, and technically
undemanding. Moreover, unreduced crystallinity of the produced nanopillars and nanopores was confirmed with Raman measurements,
which suggests their possible use as future substrates for engineering advanced nano-optoelectronic devices and sensors. 相似文献
95.
采用金属有机物化学气相沉积(MOCVD)方法生长六方相InN薄膜,利用氮化镓(GaN)缓冲层技术制备了高质量薄膜,得到了其能带带隙0.7eV附近对应的光致发光光谱(PL). 通过比较未采用缓冲层,同时采用低温和高温GaN缓冲层,以及低温GaN缓冲层结合高温退火三种生长过程,发现低温GaN缓冲层结合高温退火过程能够得到更优表面形貌和晶体质量的InN薄膜,同时表征了材料的电学性质和光学性质. 通过对InN薄膜生长模式的讨论,解释了薄膜表面形貌和晶体结构的差异. 相似文献
96.
Theodore Chung Jae Limb Jae-Hyun Ryou Wonseok Lee Peng Li Dongwon Yoo Xue-Bing Zhang Shyh-Chiang Shen Russell D. Dupuis David Keogh Peter Asbeck Ben Chukung Milton Feng Dimitri Zakharov Zusanne Lilienthal-Weber 《Journal of Electronic Materials》2006,35(4):695-700
The design and growth of GaN/InGaN heterojunction bipolar transistors (HBTs) by metalorganic chemical vapor deposition (MOCVD)
are studied. Atomic-force microscopy (AFM) images of p+InGaN base layers (∼100 nm) deposited under various growth conditions indicate that the optimal growth temperature is limited
to the range between 810 and 830°C due to a trade-off between surface roughness and indium incorporation. At these temperatures,
the growth pressure must be kept above 300 Torr in order to keep surface pit density under control. An InGaN graded-composition
emitter is adopted in order to reduce the number of V-shaped defects, which appear at the interface between GaN emitter and
InGaN base and render an abrupt emitter-base heterojunction nearly impossible. However, the device performance is severely
limited by the high p-type base contact resistance due to surface etching damage, which resulted from the emitter mesa etch. 相似文献
97.
Z. -Q. Fang D. C. Look A. Krtschil A. Krost F. A. Khan I. Adesida 《Journal of Electronic Materials》2006,35(4):613-617
Extended defects on the top surface of a 250-μm-thick free-standing GaN sample, grown by hydride vapor phase epitaxy (HVPE),
were studied by deep level transient spectroscopy (DLTS) and scanning surface potential microscopy (SSPM). For comparison,
similar studies were carried out on as-grown HVPE-GaN samples. In addition to the commonly observed traps in as-grown HVPE-GaN,
the DLTS measurements on free-standing GaN reveal a very high concentration of deep traps (∼1.0 eV) within about 300 nm of
the surface. These traps show nonexponential capture kinetics, reminiscent of those associated with large defects, that can
accumulate multiple charges. The SSPM measurements clearly reveal the presence of charged microcracks on the top surface of
the sample. It appears that the “giant traps” may be associated with these microcracks, but we cannot rule out the involvement
of other extended defects associated with the near-surface damage caused by the polishing/etching procedure. 相似文献
98.
用透射电子显微镜(TEM)和X射线双晶衍射仪(DCXRD)对在Si(111)衬底上生长的InGaN/GaN多量子阱(MQW)LED外延材料的微结构进行了观察和分析.从TEM高分辨像观察到,在Si和AlN界面处未形成SixNy非晶层,在GaN/AlN界面附近的GaN上有堆垛层错存在,多量子阱的阱(InGaN)和垒(GaN)界面明锐、厚度均匀;TEM和DCXRD进一步分析表明MQW附近n型GaN的位错密度为10acm-2量级,其中多数为b=1/3〈112-0〉的刃位错. 相似文献
99.
Z. Y. Xie C. H. Wei S. F. Chen S. Y. Jiang J. H. Edgar 《Journal of Electronic Materials》2000,29(4):411-417
The correlation between surface morphological properties of the GaN epilayers and the surface conditions of 6H-SiC (0001)
substrates etched in H2, C2H4/H2, and HCl/H2 was studied. Etching 6H-SiC in H2 produced a high quality surface with steps and terraces, while etching in HCl/H2 produced either a rough surface with many pits and hillocks or a smooth surface similar to that etched in H2, depending on the HCl concentration and temperature. The GaN epilayers were subsequently deposited on these etched substrates
using either a low temperature GaN or a high temperature AlN buffer layer via MOCVD. The substrate surface defects increased
the density and size of the “giant” pinholes (2–4 μm) on GaN epilayers grown on a LT-GaN buffer layer. Small pinholes (<100
nm) were frequently observed on the samples grown on a HT-AlN buffer layer, and their density decreased with the improved
surface quality. The non-uniform GaN nucleation caused by substrate surface defects and the slow growth rate of
planes of the islands were responsible for the formation of “giant” pinholes, while the small pinholes were believed to be
caused by misfit dislocations. 相似文献
100.
在蓝宝石衬底上低压MOVPE生长GaN单晶 总被引:5,自引:0,他引:5
研究用水平反应室低压金属有机物汽相外延方法在C面及R面蓝宝石衬上外延生长CaN单晶。讨论了反应室中气流分布和汽相反应对GaN外延生长的影响提出了不同的衬底晶向对外延GaN表面形貌产生影响的机制。 相似文献