全文获取类型
收费全文 | 1262篇 |
免费 | 688篇 |
国内免费 | 111篇 |
专业分类
化学 | 224篇 |
晶体学 | 97篇 |
力学 | 82篇 |
综合类 | 14篇 |
数学 | 388篇 |
物理学 | 1256篇 |
出版年
2024年 | 3篇 |
2023年 | 11篇 |
2022年 | 40篇 |
2021年 | 34篇 |
2020年 | 34篇 |
2019年 | 35篇 |
2018年 | 46篇 |
2017年 | 69篇 |
2016年 | 74篇 |
2015年 | 60篇 |
2014年 | 120篇 |
2013年 | 163篇 |
2012年 | 131篇 |
2011年 | 153篇 |
2010年 | 128篇 |
2009年 | 111篇 |
2008年 | 100篇 |
2007年 | 103篇 |
2006年 | 129篇 |
2005年 | 92篇 |
2004年 | 84篇 |
2003年 | 59篇 |
2002年 | 60篇 |
2001年 | 48篇 |
2000年 | 45篇 |
1999年 | 23篇 |
1998年 | 14篇 |
1997年 | 22篇 |
1996年 | 9篇 |
1995年 | 11篇 |
1994年 | 8篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1974年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有2061条查询结果,搜索用时 308 毫秒
121.
E. Richter U. ZeimerS. Hagedorn M. WagnerF. Brunner M. WeyersG. Tränkle 《Journal of Crystal Growth》2010,312(18):2537-2541
The boule-like growth of GaN in a vertical AIXTRON HVPE reactor was studied. Extrinsic factors like properties of the starting substrate and fundamental growth parameters especially the vapor gas composition at the surface have crucial impact on the formation of inverse pyramidal defects. The partial pressure of GaCl strongly affects defect formation, in-plane strain, and crystalline quality. Optimized growth conditions resulted in growth rates of 300–500 μm/h. GaN layers with thicknesses of 2.6 and of 5.8 mm were grown at rates above 300 μm/h. The threading dislocation density reduces with an inverse proportionality to the GaN layer thickness. Thus, it is demonstrated that growth rates above 300 μm/h are promising for GaN boule growth. 相似文献
122.
Kuei-Ming Chen Yen-Hsien Yeh Yin-Hao Wu Chen-Hao Chiang Din-Ru Yang Chu-Li Chao Tung-Wei Chi Yen-Hsang Fang Jenq-Dar Tsay Wei-I Lee 《Journal of Crystal Growth》2010,312(24):3574-3578
The bowing curvature of the free-standing GaN substrate significantly decreased almost linearly from 0.67 to 0.056 m−1 (i.e. the bowing radius increased from 1.5 to 17.8 m) with increase in inductively coupled plasma (ICP) etching time at the N-polar face, and eventually changed the bowing direction from convex to concave. Furthermore, the influences of the bowing curvature on the measured full width at half maximum (FWHM) of high-resolution X-ray diffraction (HRXRD) in (0 0 2) reflection were also deduced, which reduced from 176.8 to 88.8 arcsec with increase in ICP etching time. Decrease in the nonhomogeneous distribution of threading dislocations and point defects as well as VGa–ON complex defects on removing the GaN layer from N-polar face, which removed large amount of defects, was one of the reasons that improved the bowing of the free-standing GaN substrate. Another reason was the high aspect ratio of needle-like GaN that appeared at the N-polar face after ICP etching, which released the compressive strain of the free-standing GaN substrate. By doing so, crack-free and extremely flat free-standing GaN substrates with a bowing radius of 17.8 m could be obtained. 相似文献
123.
Ren-Bing Tan Wen Xu Yu Zhou Xiao-Yu Zhang Hua Qin 《Physica B: Condensed Matter》2012,407(21):4277-4280
We present a theoretical study of electron transport properties of two-dimensional electron gas in AlGaN/GaN heterostructures. By assuming a drifted Fermi–Dirac distribution and taking into account all major scattering mechanisms, including polar optical and acoustic phonons, background impurities, dislocation and interface roughness, the momentum- and energy-balance equations derived from Boltzmann equation are solved self-consistently. The dependence of the electron drift velocity and electron temperature as a function of the applied electric field are obtained and discussed. 相似文献
124.
Yoshitaka Nakano Yoshihiro Irokawa Yasunobu Sumida Shuichi Yagi Hiroji Kawai 《固体物理学:研究快报》2010,4(12):374-376
We have investigated electronic deep levels in two AlGaN/GaN hetero‐structures with different current collapses grown at 1150 and 1100 °C by a photo‐capacitance spectroscopy technique, using Schottky barrier diodes. Three specific deep levels located at ~2.07, ~2.80, and ~3.23 eV below the conduction band were found to be significantly enhanced for severe current collapse, being in reasonable agreement with photoluminescence and capacitance–voltage characteristics. These levels probably originate in Ga vacancies and residual C impurities and are probably responsible for the current collapse phenomena of the AlGaN/GaN hetero‐structures. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
125.
Steady-state nonlinear differential equations govering the stem curve of a wind-loaded pine are derived and solved numerically. Comparison is made between the results computed and the data from photographs of a pine stem during strong wind. The pine breaking is solved at the end. 相似文献
126.
1NumberandDistributionofCriticalPoilltsConsiderthefollowingcubicsystem:itcontainsonlytwocubictermspx'andqx'morethanthegeneralquadraticsystem:Thecoordinatesofthecriticalpointsatinfinityof(1)mustsatisfytheequation:px'y~qx'=0.(3)SoA(P,q,0)andB(0,l,0)aretheonlycriticalpointsatinfinityof(1).Itiseasilyseenthatthetwocharacteristicrootsof(1)atAareAl=AZ=--p,soAisastable(unstable)nodewhenp>0(<0).Moreover,Bisahigherordercriticalpointatinfinityof(1)withindex0,itisthepileupof3criticalpointsontheequat… 相似文献
127.
通过分层立方网络HCNn (n≥3)的容错性分析,从理论上探讨了分层立方网络基于比较模型的条件诊断度,并证明其条件诊断度为tc(HCNn)=3n?2,大约是传统诊断度(t(HCNn)=n+1)的3倍. 相似文献
128.
S. Ben Rejeb A. Bhouri M. Debbichi J.-L. Lazzari M. Said 《Superlattices and Microstructures》2011,50(4):277-288
Reliable and precise knowledge about the strain and composition effects on the band structure properties is crucial for the optimization of InGaN based heterostructures for electronic and optoelectronic device applications. AlInGaN as quaternary barrier material permits to control the band gap and the lattice constant independently. Using the model solid theory and the multi-band k.p interaction model, we investigate the composition effects on band offsets and band structure for pseudomorphic Ga1−xInxN/AlzInyGa1−y−zN (0 0 1) heterointerfaces having zinc-blende structure. The results show that both conduction and valence band states are strongly modified while varying In and Al contents in the well and barrier materials. Furthermore, it is found that using AlInGaN as the barrier material allows the design of heterostructures including InGaN wells with tensile, zero or compressive strain. Such results give new insights for III-nitride compounds based applications and especially may guide the design of white-light emission diodes. 相似文献
129.
130.
A. V. Astashenok A. A. Zaitsev 《Computational Mathematics and Mathematical Physics》2008,48(4):688-691
The influence of cubic nonlinearity on the dispersion relation for long waves on a water surface is analyzed. In the long wavelength limit, it is shown that the dispersion relation is not affected by the cubic terms. The results are compared with the dispersion relation for stationary solutions to the Korteweg—de Vries equation. 相似文献