全文获取类型
收费全文 | 203篇 |
免费 | 145篇 |
国内免费 | 45篇 |
专业分类
化学 | 85篇 |
晶体学 | 14篇 |
力学 | 4篇 |
数学 | 4篇 |
物理学 | 286篇 |
出版年
2024年 | 4篇 |
2023年 | 15篇 |
2022年 | 32篇 |
2021年 | 29篇 |
2020年 | 19篇 |
2019年 | 19篇 |
2018年 | 16篇 |
2017年 | 24篇 |
2016年 | 17篇 |
2015年 | 8篇 |
2014年 | 19篇 |
2013年 | 18篇 |
2012年 | 26篇 |
2011年 | 18篇 |
2010年 | 15篇 |
2009年 | 11篇 |
2008年 | 14篇 |
2007年 | 16篇 |
2006年 | 14篇 |
2005年 | 12篇 |
2004年 | 11篇 |
2003年 | 2篇 |
2002年 | 5篇 |
2001年 | 11篇 |
2000年 | 3篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 2篇 |
1993年 | 2篇 |
1990年 | 1篇 |
排序方式: 共有393条查询结果,搜索用时 15 毫秒
71.
Multiferroic NiFe2O4 (NFO)-BaTiO3 (BTO) bilayered thin films are epitaxially grown on (001) Nb-doped SrTiO3 (STO) substrates by pulsed-laser deposition (PLD). Different growth sequences of NFO and BTO on the substrate yield two kinds of epitaxial heterostructures with (001)-orientation, i.e. (001)-NFO/(001)-BTO/substrate and (001)- BTO/(001)-NFO/substrate. Microstructure studies from x-ray diffraction (XRD) and electron microscopies show differences between these two heterostructures, which result in different multiferroic behaviours. The heterostructured composite films exhibit good coexistence of both ferroelectric and ferromagnetic properties, in particular, obvious magnetoelectric (ME) effect on coupling response. 相似文献
72.
73.
染料污染是水污染中最严重的问题之一,吸引了很多科学家的关注.人们尝试了很多方法去解决该问题,如化学氧化法、物理吸附法、光催化降解法和生物降解法等.与其他几种方法相比,光催化法有着低能耗、环保以及高效等优势.三氧化钨是常见的半导体材料,具有独特的光学性能,近年来受到了广泛的研究.本文以钨酸钠和硫脲为前驱体,通过水热法制备了三氧化钨/氧化银(WO_3/Ag_2O)复合材料,并用光催化降解亚甲基蓝来分析其光催化性能.通过X射线光电子能谱、X射线衍射、透射电子显微镜、扫描电子显微镜、紫外可见吸收光谱等表征手段对样品的形貌、晶格结构和光催化的性能进行表征.氧化银的带宽为1.2 e V,对可见光很敏感,三氧化钨和氧化银的复合使材料在可见光下的光催化活性显著增强,在可见光下对亚甲基蓝染料的光降解率可以达到98%.实验结果表明,复合材料中的三氧化钨纳米棒为六方相,其平均直径约为200 nm,平均长度约为4μm.而复合材料中的氧化银纳米颗粒为六方相,附着在氧化钨纳米棒的表面,平均晶粒尺寸为20 nm.氧化银的存在为复合材料提供了更多的反应活性位点.相较于单一组分,复合材料在可见光下的光吸收度更高,这说明三氧化钨和氧化银的复合改变了材料的能带结构.研究发现,三氧化钨和氧化银之间形成的异质结构是其优良光催化性能的来源.此外,三氧化钨和氧化银复合材料还具有良好的催化稳定性和化学稳定性.本文结果表明,可以通过给宽带隙的半导体材料复合一些带隙合适的金属氧化物以提升其光催化活性. 相似文献
74.
The problem of electron resonant and non-resonant scatterings on two magnetized barriers is studied in the one-dimension. The transfer-matrix is built up to exactly calculate the coefficient of the electron transmittance through the system of two magnetic barriers with non-collinear magnetizations. The polarization of the transmitted electron wave for resonance and non-resonance transmittances is calculated. The transmittance coefficient and spin polarization can be drastically enhanced and controlled by the angle between the barrier magnetizations. 相似文献
75.
论文根据ZnMgO/ZnO异质结构二维电子气的能带结构及相关理论模型, 采用一维Poisson-Schrodinger方程的自洽求解, 模拟计算了ZnMgO/ZnO异质结构中二维电子气的分布及其对ZnMgO势垒层厚度及Mg组分的依赖关系. 研究发现该异质结构中ZnMgO势垒层厚度存在一最小临界值: 当垒层厚度小于该临界值时, 二维电子气消失, 当垒层厚度大于该临界值时, 其二维电子气密度随着该垒层厚度的增加而增大; 同时研究发现ZnMgO势垒层中Mg组分的增加将显著增强其二维电子气的行为, 导致二维电子气密度的明显增大; 论文对模拟计算获得的结果与相关文献报道的实验结果进行了比较, 并从极化效应和能带结构的角度进行了分析和讨论, 给出了合理的解释.
关键词:
氧化锌
二维电子气
异质结构
理论计算 相似文献
76.
Spin‐polarized density functional theory is used to study the TiO2 terminated interfaces between the magnetic Heusler alloys Co2Si (M = Ti, V, Cr, Mn, and Fe) and the non‐polar band insulator SrTiO3. The structural relaxation at the interface turns out to depend systematically on the lattice mis‐ match. Charge transfer from the Heusler alloys (mainly the M 3d orbitals) to the Ti dxy orbitals of the TiO2 interface layer is found to gradually grow from M = Ti to Fe, resulting in an electron gas with increasing density of spin‐polarized charge carriers. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
77.
Effects of SiNx on two-dimensional electron gas and current collapse of AlGaN/GaN high electron mobility transistors 下载免费PDF全文
SiN_x is commonly used as a passivation material for
AlGaN/GaN high electron mobility transistors (HEMTs). In this paper,
the effects of SiN_x passivation film on both two-dimensional
electron gas characteristics and current collapse of AlGaN/GaN HEMTs
are investigated. The SiN_x films are deposited by high- and
low-frequency plasma-enhanced chemical vapour deposition, and they
display different strains on the AlGaN/GaN heterostructure, which
can explain the experiment results. 相似文献
78.
V. P. Veleshchuk O. V. Lyashenko Yu. A. Myagchenko R. G. Chuprina 《Journal of Applied Spectroscopy》2004,71(4):553-557
The dependence of the spectral position of the electroluminescence bands of epitaxial light-emitting diode n
+–n–p structures (GaAs0.15P0.85) on the density of a direct heterojunction current at different successive instants of time — before an acoustic emission and after it — has been revealed. The shifts of the electroluminescence bands accompanied by acoustic emission can be divided into three types according to the density of the current: (1) short-term shifts due to relaxation of the defect structure of a sample — at relatively low currents, (2) the magnitude of the reverse shift being determined by the current density — at large currents, and (3) formation of an IR band (1.5–1.1 eV) with irreversible degradation changing in the red (1.75 eV) and green (2.19 eV) bands of the electroluminescence spectrum — at ultrahigh currents (100–200 A/cm2). 相似文献
79.
Junsaku Nitta Yiping Lin Takaaki Koga Tatsushi Akazaki 《Physica E: Low-dimensional Systems and Nanostructures》2004,20(3-4):429
We report on electron g-factor in an InAs-inserted In0.53Ga0.47As/In0.52Al0.48As heterostructure. The gate voltage dependence of g-factor is obtained from the coincidence method. The obtained g-factor values are surprisingly smaller than the g-factor value of bulk InAs, and it is close to the bare g-factor value of In0.53Ga0.47As. The large change in g-factor is observed by applying the gate voltage. The obtained gate voltage dependence is not simply explained by the energy dependence of g-factor. 相似文献
80.
We study the technology of local anodic oxidation (LAO) by the AFM tip applied to semiconductor heterostructures with two-dimensional electron gas. The aim is to design mesoscopic rings with persistent current and one subband occupied. For this purpose the need is to oxidize narrow lines that represent energy barriers high enough. Using the electrostatic model, we explain the electric field distribution in the system tip-sample just before LAO starts. We study the influence of the conductivity of the cap layer on LAO and explain the origin of the saddle-like profile lines, observed in the experiment. Using Monte Carlo simulation we show that the carrier redistribution in the system with LAO energy barriers effectively lowers the barrier height. In the experimental part we have grown InGaP/AlGaAs/GaAs heterostructures by organometalic vapor phase epitaxy with an active layer only 31 nm below the surface. We have prepared oxide lines on the heterostructures by LAO and characterized them by the temperature-dependent transport measurement. 相似文献