全文获取类型
收费全文 | 668篇 |
免费 | 166篇 |
国内免费 | 33篇 |
专业分类
化学 | 43篇 |
晶体学 | 50篇 |
力学 | 1篇 |
综合类 | 2篇 |
数学 | 3篇 |
物理学 | 623篇 |
综合类 | 145篇 |
出版年
2024年 | 1篇 |
2023年 | 3篇 |
2022年 | 11篇 |
2021年 | 6篇 |
2020年 | 5篇 |
2019年 | 12篇 |
2018年 | 13篇 |
2017年 | 15篇 |
2016年 | 21篇 |
2015年 | 17篇 |
2014年 | 34篇 |
2013年 | 46篇 |
2012年 | 37篇 |
2011年 | 40篇 |
2010年 | 37篇 |
2009年 | 37篇 |
2008年 | 31篇 |
2007年 | 40篇 |
2006年 | 59篇 |
2005年 | 42篇 |
2004年 | 42篇 |
2003年 | 26篇 |
2002年 | 49篇 |
2001年 | 21篇 |
2000年 | 49篇 |
1999年 | 18篇 |
1998年 | 22篇 |
1997年 | 27篇 |
1996年 | 17篇 |
1995年 | 11篇 |
1994年 | 16篇 |
1993年 | 11篇 |
1992年 | 13篇 |
1991年 | 7篇 |
1990年 | 11篇 |
1989年 | 2篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1974年 | 1篇 |
排序方式: 共有867条查询结果,搜索用时 0 毫秒
91.
Fanyao Qu N. O. Dantas P. C. Morais 《Physica E: Low-dimensional Systems and Nanostructures》2001,9(4):709
The investigation of the evolution of the photoluminescence spectra, in single asymmetric quantum wells (SAQWs), from a typical emission spectrum to a Fermi-edge singularity, is carried out as a function of both the optical excitation intensity and the temperature. The three samples used here are n-doped, low carrier density (below 5×1011 cm−2), GaAs/Al0.35Ga0.65As SAQWs grown by molecular beam epitaxy. The strong collective recombination of electrons with different k states up to the Fermi wave vector as well as the optical signature of the Fermi-edge singularity is observed in two samples containing residual acceptors inside the GaAs SAQW. In contrast, a third sample containing no experimental evidence of residual acceptors in the GaAs SAQW shows no optical signature of the Fermi-edge singularity. 相似文献
92.
93.
The behaviour of the latent image produced by actinic radiation (λ = 365 nm and λ = 407 nm) in AgCl monocrystal foils highly doped with Cd and grown and annealed under various conditions was studied by extinction measurements in the near infrared. The photographic elementary process in these highly doped crystals cannot be described satisfactorily by the classical Gurney Mott model. Therefore another model was used based on the creation of anion vacancies and molecular chlorine complexes. The radiation-induced electrons occupy these anion vacancies, and quasi- metallic centres are formed. By this model the behaviour of the light-induced latent image can also be described as the nuclear particle track formation in the Cd doped AgCl crystals. 相似文献
94.
为了实现光阴极光谱响应向短波延伸,分析了Ga1-xAlxAs/GaAs三代微光光阴极光谱响应向短波延伸的机理,提出了准禁带宽度的概念,讨论了Ga1-xAlxAs的禁带宽度随铝组份x值的增加而逐渐变宽的变化规律,计算了不同铝组份下光阴极光谱响应的短波限。通过提高光阴极材料的铝组份,做出了宽光谱响应像管,并给出了相应的光谱响应曲线。通过与标准三代微光像管光谱响应对比,发现:所得光谱响应曲线不仅向短波方向得以延伸,而且理论设计与实验结果吻合很好。 相似文献
95.
采用分解GaP这一新型固态P源分子束外延在GaAs衬底成功制备了InGaP外延薄膜.3μm厚的InGaP外延层低温荧光峰位是1.998 eV,半峰宽为5.26 meV.双晶摇摆曲线的线宽同GaAs衬底相近.霍尔测量非故意掺杂InGaP外延层的室温迁移率同其他源或其他方法生长的外延层结果类似. 相似文献
96.
M. Karl D. RülkeT. Beck D.Z. HuD.M. Schaadt H. KaltM. Hetterich 《Superlattices and Microstructures》2010
Pyramidal micro-cavities represent a novel promising class of semiconductor optical cavities. In contrast to our previous approach based on pyramids sitting on distributed Bragg reflectors, we investigate reversed freestanding GaAs pyramids. The latter are achievable by a wet-chemical etching process where an AlAs sacrificial layer in the epitaxially grown layer structure is used. In freestanding GaAs pyramids, light is simply confined by total internal reflection at the interface of the high refractive index material GaAs to the surrounding. Due to strong optical confinement within the pyramidal shape, small mode volumes are expected. Quality factors up to 3000 were measured in first structures. However, simulations suggest the possibility of much higher values. Therefore, these freestanding pyramids are promising for an optimized ratio between quality factor and mode volume, which is crucial for quantum-optical applications. 相似文献
97.
对由Al_yGa_(1-y_As,Al_xGa_(1-x)As和GaAs三种材料构成的超晶格价带的自旋劈裂进行了研究.通过改变材料组分和层厚,发现当超晶格单胞对其中心点是不对称结构时,对应的自族向上和自族向下的子带产生劈裂,而且劈裂主要发生在重空穴带和轻空穴带相互作用较强的地方. 相似文献
98.
We report a photoluminescence detected anticrossing of the energy levels in an undoped asymmetric coupled-double-quantum-well buried in a p-i-n structure. Due to the built-in electric field, the quantum wells are tilted in such a way that the symmetric energy level is higher than that of the antisymmetric one in the conduction band. Keeping the laser excitation energy below the barrier, with increasing laser power, the level anticrossing and the quantum confined Stark effect were observed due to decreasing built-in electric field by the photogenerated electron and hole pairs. 相似文献
99.
Photoelectron spectroscopy, in particular the angular resolved photoemission excited by ultraviolet radiation (ARUPS), provides the most direct experimental information about the electron structure of crystals, both of the bulk and of the low-index surfaces. The sensitivity of the method, as well as its difficulties, when applied to GaAs/AlAs superlattices are described. The new periodicity of these man-made crystals in the direction of their growth (e.g., in the layer-by-layer growth in molecular beam epitaxy), is responsible for opening of the new energy gaps (so-called minigaps) in the electron energy bands of crystals forming the superlattice. In addition to the well-known confinement of electrons at the valence and conduction band edges in long-period superlattices, the electron confinement to the interfaces has also been found in the vicinity of minigaps in short-period superlattices. The role of this confinement in the intensities of electrons photoemitted from superlattice surfaces is discussed. Superlattices with different thicknesses in the topmost layers represent systems with a simple change of the surface atomic structure. The predictions of one-dimensional models about a change of the surface-state energy within the band gap with a change of crystal potential termination are tested for the ideally terminated (1 0 0) surface of a very thin superlattice (GaAs)2(AlAs)2. The results of the energy distributions of photoemitted electrons, calculated in the one-step model of photoemission, show that the ARUPS experimental observation of surface-state shifts should be possible, at least in larger minigaps. The results indicate the possibility of a straightforward tuning of the electronic structure of the superlattice surface by geometrical means. 相似文献
100.
Harry J. Whitlow Margaretha Andersson Mikael Hult Leif Persson Mohamed El Bouanani Mikael Östling Carina Zaring Nils Lundberg David D. Cohen Nick Dytlewski Peter N. Johnston Ian F. Bubb Scott R. Walker Erik Johanson Sture Hogmark P. Anders Ingemarsson 《Mikrochimica acta》1995,120(1-4):171-181
Recoil Spectrometry covers a group of techniques that are very similar to the well known Rutherford backscattering Spectrometry technique, but with the important difference that one measures the recoiling target atom rather than the projectile ion. This makes it possible to determine both the identity of the recoil and its depth of origin from its energy and velocity, using a suitable detector system. The incident ion is typically high-energy (30–100MeV)35C1,81Br or127I. Low concentrations of light elements such as C, O and N can be profiled in a heavy matrix such as Fe or GaAs. Here we present an overview of mass and energy dispersive recoil Spectrometry and illustrate its successful use in some typical applications. 相似文献