全文获取类型
收费全文 | 165篇 |
免费 | 27篇 |
国内免费 | 29篇 |
专业分类
化学 | 70篇 |
晶体学 | 75篇 |
力学 | 3篇 |
综合类 | 2篇 |
数学 | 4篇 |
物理学 | 67篇 |
出版年
2022年 | 1篇 |
2021年 | 6篇 |
2020年 | 6篇 |
2019年 | 6篇 |
2018年 | 6篇 |
2016年 | 2篇 |
2015年 | 2篇 |
2014年 | 7篇 |
2013年 | 18篇 |
2012年 | 10篇 |
2011年 | 13篇 |
2010年 | 7篇 |
2009年 | 11篇 |
2008年 | 11篇 |
2007年 | 4篇 |
2006年 | 3篇 |
2005年 | 25篇 |
2004年 | 24篇 |
2003年 | 13篇 |
2002年 | 20篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1999年 | 6篇 |
1998年 | 1篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 4篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1990年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有221条查询结果,搜索用时 15 毫秒
21.
We investigate the isothermal annealing of E′ centers generated by UV photons (266 nm) of a pulsed Nd:YAG laser in two natural silica types differing for their OH content. Electron spin resonance and absorption spectra recorded at room temperature at different delays from the laser exposure evidenced a partial reduction of E′ centers, more pronounced in the wet silica. These post irradiation kinetics complete within 105 s, regardless the silica type, and they are consistent with a diffusion limited reaction between the E′ centers and the molecular hydrogen H2. Analysis of our data is done by theoretical fits using the Waite's equation and compared with the H2 diffusion parameters reported in literature. Finally, the interplay between the under radiation generation and the post irradiation annealing of E′ centers was investigated through repetitive laser exposures, which evidenced the higher resistance of wet silica to induced laser damage. 相似文献
22.
Amorphous and polycrystalline (Pb0.76Ca0.24)TiO3 (PCT) thin films deposited on an Si(1 0 0) substrate have been prepared by a simple sol-gel process. The microstructure and surface morphologies of the thin films have been studied by X-ray diffraction (XRD) and atomic force microscopy (AFM). The polycrystalline PCT film on the Si(1 0 0) substrate has a tetragonal perovskite structure with grain size from 60 to 110 nm. AFM reveals smooth surfaces and root mean square (rms) roughness of 0.17 and 4.4 nm for amorphous and polycrystalline films, respectively. The refractive index n and extinction coefficient k of the amorphous and polycrystalline thin films was obtained by spectroscopic ellipsometry as a function of the photon energy in the range from 2.0 to 5.4 eV. The maximum n and direct bandgap energies of amorphous and polycrystalline thin films were 2.66 and 4.11 eV, 2.64 and 3.84 eV, respectively. 相似文献
23.
We present the results of plane wave density functional theory calculations of oxygen vacancies and interstitial oxygen atoms in monoclinic zirconia. After calculating the incorporation energies and structures of interstitial oxygen atoms and formation energies of neutral oxygen vacancies, we consider the electron affinities and ionisation potentials of these defects. These properties are especially important at the silicon/oxide interface in MOSFET devices, where silicon may serve as an electron and hole source. The results demonstrate that interstitial oxygen atoms and positively charged oxygen vacancies can trap electrons if the electron source (band offset) is higher than ∼2 eV above the top of the zirconia valence band. 相似文献
24.
Zinc underpotential deposition (Zn UPD) was studied by cyclic voltammetry in solutions of various pH and composition, where
the effects of the presence of boric acid or chloride in the solution were observed. We have found that the cyclic voltammograms
of Zn UPD at Pt(111) were dependent on boric acid concentrations, zinc ion concentrations, and pH in acidic solutions. These
suggest that the induced adsorption of borate by releasing of H+ is accompanied with Zn UPD. The preadsorbed chloride species on Pt(110) accelerate the UPD process by their removal just
before the UPD, making the surface sites available for the process, and the UPD remains at identical electrode potentials,
while the chloride ions do not take part in the induced adsorption on UPD Zn at Pt, as clearly found by the radiotracer method.
These show that the anions play versatile roles in the process of adlayer formation by their different but essential chemical
characteristics.
Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 6, pp. 745–751
The text was submitted by the authors in English. 相似文献
25.
Shin SatohIwao Matsuyama 《Journal of Non》2002,306(3):300-308
Tantalum-doped silica glass was fabricated by the sol-gel process in order to obtain a glass with a high refractive index for optical use. A crack-free, clear glass rod was successfully prepared from a low-density gel and used as the core material for fabricating optical fibers. Transmission loss in the fabricated fibers was high, in the range of 103-104 dB/km, which may be caused by coloration due to the multivalency of tantalum; however, the loss was reduced by nearly one order of magnitude by heat treatment at 800 °C, that is, to 75 dB/km at a wavelength of 0.8 μm. 相似文献
26.
The microstructure evolution of decagonal quasicrystals in Al72Ni12Co16 alloy was investigated by the electromagnetic melting and cyclic superheating method. Single-phase decagonal quasicrystals have been obtained when the undercoolings were larger than 60 K. The decagonal quasicrystals formed at various undercoolings show different microstructural morphologies. Furthermore, grain refinement was found near the undercooling of 120 K. Based on current thermodynamic and dendrite growth theories, a dimensionless superheating parameter was adopted to explain the effect of processing conditions on the microstructure of Al72Ni12Co16 alloy. The result indicate that the fine equiaxied microstructure of decagonal quasicrystal (D-phase) formed near on undercooling of 120 K originates from the break-up of dendrites. 相似文献
27.
H. Nohira W. TsaiW. Besling E. YoungJ. Petry T. Conard W. VandervorstS. De Gendt M. HeynsJ. Maes M. Tuominen 《Journal of Non》2002,303(1):83-87
The atomic layer chemical vapor deposition (ALCVD) deposited Al2O3 and ZrO2 films were investigated by ex situ X-ray photoelectron spectroscopy. The thickness dependence of band gap and valence band alignment was determined for these two dielectric layers. For layers thicker than 0.9 nm (Al2O3) or 0.6 nm (ZrO2), the band gaps of the Al2O3 and ZrO2 films deposited by ALCVD are 6.7±0.2 and 5.6±0.2 eV, respectively. The valence band offsets at the Al2O3/Si and ZrO2/Si interface are determined to be 2.9±0.2 and 2.5±0.2 eV, respectively. Finally, the escape depths of Al 2p in Al2O3 and Zr 3p3 in ZrO2 are 2.7 and 2.0 nm, respectively. 相似文献
28.
The virtual microstructures relevant to lithiumdisilicate glass crystallization have been created as an environment to compute the light scattering. The input data in computations include the number density of crystals, refractive indices of involved glassy and crystalline phases, the wavelength of the incident beam radiation, and the virtual sample slab thickness. The computations are performed under a number of simplifying conditions. They treat cases with proposed constant number densities of crystals, assuming their random volume distribution. The shape of the crystals is approximated by spheres. The results are expressed graphically in the form of theoretical optical transmission (OT) patterns, as they evolve on the crystal size axis. They reveal an influence of input data on computed OT. As evident from computations, some sets of input data will favor the real OT method's detection limits. The opposed sets of data will aid following the crystallization to the higher sample crystallinity degree α. 相似文献
29.
Using two versions of the first principles full potential linear muffin-tin orbitals method (FPLMTO) which enable an accurate treatment of the interstitial regions, the electronic and optical properties of (110) growth axis Si/SiGe superlattices are investigated. A comparative study with (001) growth axis superlattices is made. In particular, it is found that the bottom of the conduction band (CB) is closer to Γ in the (110) system but the optical activity is not enhanced. Furthermore, the absorption spectra of the superlattices are calculated and are found to be quite different from those of bulk Si and Ge but fairly close to their average. 相似文献
30.
通过对129I加速器质谱(AMS)分析中影响敏度和准确度各种参数的研究,如靶电极制备、压样、靶样中辅助介质(Matrix)的选择及使用比例等,优化了用于3 MV加速器质谱仪的SO-110型离子源的条件参数,确定129I-AMS测量的最佳靶电极材料为Cu,最佳的辅助介质为Nb粉末,Nb与AgI样品的最佳体积比为3∶1。在此条件下可以获得稳定且持续的I-束流进行测量129I/127I原子比值,实验测得西安加速器质谱仪的129I/127I本底值为1.5210-14。 相似文献