全文获取类型
收费全文 | 570篇 |
免费 | 581篇 |
国内免费 | 37篇 |
专业分类
化学 | 74篇 |
晶体学 | 87篇 |
力学 | 3篇 |
综合类 | 5篇 |
数学 | 7篇 |
物理学 | 1012篇 |
出版年
2024年 | 3篇 |
2023年 | 7篇 |
2022年 | 27篇 |
2021年 | 24篇 |
2020年 | 13篇 |
2019年 | 12篇 |
2018年 | 24篇 |
2017年 | 43篇 |
2016年 | 58篇 |
2015年 | 41篇 |
2014年 | 83篇 |
2013年 | 97篇 |
2012年 | 96篇 |
2011年 | 122篇 |
2010年 | 81篇 |
2009年 | 67篇 |
2008年 | 58篇 |
2007年 | 57篇 |
2006年 | 76篇 |
2005年 | 49篇 |
2004年 | 41篇 |
2003年 | 26篇 |
2002年 | 29篇 |
2001年 | 21篇 |
2000年 | 15篇 |
1999年 | 10篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1995年 | 2篇 |
排序方式: 共有1188条查询结果,搜索用时 15 毫秒
991.
Although significant progress has been achieved in GaN based high power/high frequency electronic devices, surface-related problems still need an immediate solution. In particular, leakage currents through Schottky contacts not only impede device reliability but also degrade power efficiency and noise performance in such devices. This article discusses the mechanism of leakage currents through GaN Schottky and AlGaN/GaN Schottky interfaces for both forward and reverse biases. A theoretical model for the calculation of currents based on trap-assisted tunneling is discussed. In the calculation the trap energy has been assumed as a fitting parameter which is about 0.48 eV for different Al mole fractions. The comparison of the results obtained with the existing experimental data in the literature shows a good agreement. 相似文献
992.
T. Nakaoka S. Kako Y. Arakawa 《Physica E: Low-dimensional Systems and Nanostructures》2006,32(1-2):148
We have experimentally and theoretically investigated quantum confined Stark effect in hexagonal self-assembled GaN/AlN quantum dots. We have observed a blueshift of up to 100 meV for vertical electric field applied against the built-in electric field while we have observed a redshift for the electric field along the built-in field. The experimental result is compared with a charge self-consistent effective mass calculation, taking into account strain, piezoelectric charge, and pyroelectric charge. The tunability of the emission energy and the exciton binding energy is discussed. 相似文献
993.
B. Daudin C. Adelmann N. Gogneau E. Sarigiannidou E. Monroy F. Fossard J. L. Rouvire 《Physica E: Low-dimensional Systems and Nanostructures》2004,21(2-4):540
The conditions to grow GaN quantum dots (QDs) by plasma-assisted molecular beam epitaxy will be examined. It will be shown that, depending on the Ga/N ratio value, the growth mode of GaN deposited on AlN can be either of the Stranski–Krastanow (SK) or of the Frank–Van der Merwe type. Accordingly, quantum wells or QDs can be grown, depending on the desired application. In the particular case of modified SK growth mode, it will be shown that both plastic and elastic strain relaxation can coexist. Growth of GaN QDs with N-polarity will also be discussed and compared to their counterpart with Ga polarity. 相似文献
994.
995.
R. Mosca E. Gombia A. Passaseo V. Tasco M. Peroni P. Romanini 《Superlattices and Microstructures》2004,36(4-6):425
Passivating the ungated surface of AlGaN/GaN HEMTs with silicon nitride (SiN) is effective in improving the microwave output power performances of these devices. However, very little information is available about surface states in GaN-based HEMTs after SiN passivation. In this work we investigate AlGaN/GaN HEMTs structures having either metal–semiconductor or metal–SiN–semiconductor gate contacts. In short gate devices conductance DLTS measurements point out a hole-like peak that shows an anomalous behaviour and can be ascribed to surface states in the access regions of the device. In insulated gate HEMTs a band of levels is detected and ascribed to surface states, whose energy ranges from 0.14 to 0.43 eV. Capacitance–voltage measurements allow us to point out the existence of a second band of interface states deeper in energy than the former one. This band is responsible for slow transients observed in the characteristics of the insulated gate FAT-HEMT. 相似文献
996.
We have estimated the threading dislocation density and type via X-ray diffraction and Williamson-Hall analysis to elicit qualitative information directly related to the electrical and optical quality of GaN epitaxial layers grown by PAMBE on 4H- and 6H-SiC substrates. The substrate surface preparation and buffer choice, specifically: Ga flashing for SiC oxide removal, controlled nitridation of SiC, and use of AlN buffer layers all impact the resultant screw dislocation density, but do not significantly influence the edge dislocation density. We show that modification of the substrate surface strongly affects the screw dislocation density, presumably due to impact on nucleation during the initial stages of heteroepitaxy. 相似文献
997.
998.
用全势缀加平面波加局域轨道 (APW +lo)的方法计算了六方GaN及其非极性 ( 10 10 )表面的原子及电子结构 .计算出的六方GaN晶体结构参数 :晶格常数和体积弹性模量与实验值符合得很好 .用平板超原胞模型来计算GaN( 10 10 )表面的原子与电子结构 ,结果表明表面顶层原子发生键长收缩并扭转的弛豫特性 .表面阳离子向体内移动 ,趋向于sp2 平面构形 ;而表面阴离子向体外移动 ,趋向于锥形的p3构形 .弛豫后 ,表面实现由半金属性向半导体性的转变 .并且 ,表面电荷发生大的转移 ,参与表面键的重新杂化 ,使得表面原子的离子性减弱共价性增强 ,认为这就是表面原子键收缩并旋转的原因 相似文献
999.
采用低压MOCVD系统,在生长过程中使用SiNx原位淀积的方法产生纳米掩模,并 在纳米掩模上进行选区生长和侧向外延制备了GaN外延薄膜.使用拉曼光谱和光荧光的手段对 GaN外延膜中的残余应力进行了研究.研究发现,用SiNx原位淀积出纳米掩模后 ,GaN生长将由二维向三维转变,直到完全合并为止.利用拉曼光谱和光荧光谱分别研究了薄 膜中的残余应力,两者符合得很好;这种方法生长出的GaN薄膜的应力分布较传统的侧向外 延更加均匀;并且从中发现随着生长过程中SiNx原位淀积时间的增加,生长在 其上的GaN外延膜中的残余应力减小.这是因为,随着SiNx原位淀积时间的增加 ,SiNx纳米掩模的覆盖度也增大.因此侧向外延区的比例增大,残余应力随之减 小.
关键词:
GaN
x原位淀积')" href="#">SiNx原位淀积
拉曼
光荧光
残余应力 相似文献
1000.
181Hf and 111In ions were implanted into AlN-layers in order to investigate their immediate lattice site environment and its temperature
dependence by means of the Perturbed Angular Correlation (PAC) technique. After rapid thermal annealing at 1273 K up to 50%
of the probe atoms were incorporated on undisturbed lattice sites defined by an electric field gradient (EFG) of 33 MHz for
In and 572 MHz for Hf for measurement at room temperature. PAC-spectra taken at temperatures between 25 and 1200 K show that
the EFG measured at the site of the undisturbed probes changes with temperature. While for Hf it decreases by 3%, for In it
increases by 25% within the measured temperature range. Thus, the change cannot be due only to the thermal lattice expansion.
In the case of In the fraction of probe atoms on substitutional sites increases with temperature until it reaches nearly 100%
at 973 K. These effects are fully reversible. For the Hf probe, an additional EFG was detected at temperatures above 300 K. 相似文献