全文获取类型
收费全文 | 913篇 |
免费 | 144篇 |
国内免费 | 54篇 |
专业分类
化学 | 172篇 |
晶体学 | 23篇 |
力学 | 176篇 |
综合类 | 3篇 |
数学 | 24篇 |
物理学 | 713篇 |
出版年
2024年 | 1篇 |
2023年 | 7篇 |
2022年 | 15篇 |
2021年 | 13篇 |
2020年 | 15篇 |
2019年 | 13篇 |
2018年 | 15篇 |
2017年 | 23篇 |
2016年 | 36篇 |
2015年 | 39篇 |
2014年 | 47篇 |
2013年 | 57篇 |
2012年 | 43篇 |
2011年 | 71篇 |
2010年 | 44篇 |
2009年 | 72篇 |
2008年 | 48篇 |
2007年 | 74篇 |
2006年 | 62篇 |
2005年 | 46篇 |
2004年 | 78篇 |
2003年 | 68篇 |
2002年 | 29篇 |
2001年 | 32篇 |
2000年 | 36篇 |
1999年 | 21篇 |
1998年 | 23篇 |
1997年 | 18篇 |
1996年 | 17篇 |
1995年 | 6篇 |
1994年 | 8篇 |
1993年 | 8篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1990年 | 3篇 |
1988年 | 1篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1979年 | 1篇 |
排序方式: 共有1111条查询结果,搜索用时 312 毫秒
971.
Oliver Warschkow Mark Asta Kenneth R. Poeppelmeier Laurence D. Marks 《Surface science》2004,573(3):446-456
We have recently reported structure solutions for the (2 × 1) and c(4 × 2) reconstructions of SrTiO3(0 0 1) based on high-resolution electron microscopy, direct methods analysis of diffraction data and density functional theory. Both reconstructions were found to be TiO2-rich and feature a single overlayer of TiO2 stoichiometry on top of a bulk-like TiO2 layer. Qualitatively, the two reconstruction geometries differ in the cation sub-lattice of the overlayer only, where Ti atoms occupy half of the fivefold cation sites. In the present work we use density functional theory to generate a number of variations of this structural motif in search of patterns of stability. We find a reliable predictor for the reconstruction energy in the ability of oxygen atoms to relax vertically out of the overlayer plane to minimize non-bonded oxygen-oxygen repulsions. Out-of-plane relaxation of oxygen atoms in turn is modulated by the number and relative position of coordinating Ti atoms, which yields simple empirical rules as to how cations are distributed in low energy reconstructions. 相似文献
972.
Density functional theory (DFT) calculations of the calcium tungstate material scheelite CaWO4 have shown that water introduced into the bulk material remains undissociated and leads to swelling and layering of the structure, a behaviour which may resemble silicate clays more than three-dimensional poly-anionic materials, but which results in a structure that is even more similar to a rare hydrous calcium carbonate phase--a finding which suggests the existence of semi-crystalline hydrous pre-cursor phases to the dehydrated scheelite material. An interatomic potential model was derived for CaWO4 which adequately reproduces structural and physical properties of the material and is in good agreement with the DFT calculations in respect of the structure and energy of hydration (DFT: 85 kJ mol−1, atomistic: 105 kJ mol−1). Atomistic simulations of a range of scheelite surfaces confirm the dominance of the experimental {1 0 1} and {0 0 1} cleavage planes in the morphology of the dry crystal and the presence of the experimentally found {1 0 3} and {1 0 1} surfaces in the hydrated morphology. Hydration of the surfaces shows non-Langmuir behaviour, where the interactions between surface calciums and oxygen atoms of the water molecules outweigh hydrogen-bonding to the surface oxygen atoms or intermolecularly within the water layer. The hydration energies indicate physisorption of water, ranging from 22 kJ mol−1 on the {0 0 1} surface to 78 kJ mol−1 on the more reactive {1 0 3} surface. 相似文献
973.
J. Myslive
ek C. Schelling F. Schffler G. Springholz P.
milauer J. Krug B. Voigtlnder 《Surface science》2002,520(3):193-206
A scanning tunneling microscopy/atomic force microscopy study is presented of a kinetically driven growth instability, which leads to the formation of ripples during Si homoepitaxy on slightly vicinal Si(0 0 1) surfaces miscut in [1 1 0] direction. The instability is identified as step bunching, that occurs under step-flow growth conditions and vanishes both during low-temperature island growth and at high temperatures. We demonstrate, that the growth instability with the same characteristics is observed in two dimensional kinetic Monte Carlo simulation with included Si(0 0 1)-like diffusion anisotropy. The instability is mainly caused by the interplay between diffusion anisotropy and the attachment/detachment kinetics at the different step types on Si(0 0 1) surface. This new instability mechanism does not require any additional step edge barriers to diffusion of adatoms. In addition, the evolution of ripple height and periodicity was analyzed experimentally as a function of layer thickness. A lateral “ripple-zipper” mechanism is proposed for the coarsening of the ripples. 相似文献
974.
975.
The nanometer-scale indentation of a crystalline surface produces nanostructures that evolve on a timescale that is inaccessible to existing imaging methods for the vast majority of surfaces. We have been able to observe the dynamic evolution of the freshly cleaved surface of a NaCl(100) crystal after indentation with an atomic force microscope (AFM) in air. Here we present sequential AFM images featuring vertical atomic resolution which show that atomic terrace motion is greatly enhanced by the AFM indentation. Moreover, some of the nanometric features generated by the indentation become reassimilated into the crystalline surface structure of the surroundings of the indentation over a period of time of the order of several minutes. 相似文献
976.
S. Eck C. Castellarin-Cudia S. Surnev M. G. Ramsey F. P. Netzer 《Surface science》2002,520(3):173-185
Ultrathin layers of cerium oxide have been deposited on a Rh(1 1 1) surface and their growth morphology, structure, and thermal stability have been investigated by LEED, STM, XPS, and valence band resonant photoemission. STM and LEED indicate that the ceria grows epitaxially in form of ordered CeO2 islands at elevated substrate temperature (250–300 °C), with (1 1 1) faces parallel and orientationally aligned to the main azimuthal directions of the substrate. The ultrathin ceria films contain significant amounts of reduced Ce3+ species, which appear to be located predominantly at the ceria–Rh interface. For thicker films (>6 equivalent monolayers) stoichiometric CeO2 is detected in XPS. Vacuum annealing produces morphologically well-defined hexagonal islands, accompanied by partial reduction and the formation of oxygen vacancies at the ceria surface. The thermal stability and the degree of reduction is a function of the oxide layer thickness, with thinner layers being thermally less stable. At temperatures >800 °C, the ceria decomposes and Ce–Rh alloy phases are identified. 相似文献
977.
Yusser Al-Qazwini A.S.M. Noor P.T. Arasu A.R. Sadrolhosseini 《Current Applied Physics》2013,13(7):1354-1358
Finite-difference time domain (FDTD) method was used to investigate the performance of surface plasmon resonance (SPR)-based optical fiber sensors. The results show that the performance of the fiber sensor can be optimized by choosing a proper combination of metal layer thickness of 40–60 nm and residual cladding thickness of 400–500 nm. Furthermore, the roughness effect of the gold surface layering the fiber sensor is significant in rough surfaces when sigma rms is greater than 5 nm or correlation length is lower than 100 nm. 相似文献
978.
The growth of bcc crystals is studied using van Beijeren's mapping onto the six-vertex model. The growth-evaporation processes are described in terms of vertices. The time evolution is given by a master equation for the probability of the six-vertex configurations. The model, studied in the finite-size case by both Monte Carlo and analytic methods, applies to the (001) surface and its vicinal surfaces. Different growth modes (including nucleation) are found, depending on the strength of disequilibrium and on temperature, and the transition between them is investigated.On leave of absence from the Institute of Physics, Czechoslovak Academy of Science, Prague, Czechoslovakia. 相似文献
979.
Palladium overlayers deposited on TiO2(110) by metal vapour deposition have been investigated using LEED, XPS and FT-RAIRS of adsorbed CO. Low coverages of palladium (<3 ML) deposited at 300 K adsorb CO exclusively in a bridged configuration with a band (B1 at 1990 cm−1) characteristic of CO adsorption on Pd(110) and Pd(100) surfaces. When annealed to 500 K, XPS and LEED indicate the nucleation of Pd particles on which CO adsorbs predominantly as a strongly bound linear species which we associate with edge sites on the Pd particles (L* band at 2085 cm−1). Both bridged and linear CO bands are exhibited as increases in reflectivity at the resonant frequency, indicating the retention of small particle size during the annealing process. Palladium overlayers of intermediate coverages (10–20 ML) deposited at 300 K undergo some nucleation during growth, and adsorbed CO exhibits both absorption and transmission bands in the B1 (1990 cm−1) and B2 (1940 cm−1) regions. The latter is associated with the formation of Pd(111) facets. Highly dispersed Pd particles are produced on annealing at 500 K. This is evidenced by the dominance of transmission bands for adsorbed CO and a significant concentration of edge sites, which accommodate the strongly bound linear species at 300 K. Adsorption of CO at low temperature also allows the identification of the constituent faces of Pd and the conversion of Pd(110)/(100) facets to Pd(111) facets during the annealing process. High coverages of palladium (100 ML) produce only absorption bands in FT-RAIRS of adsorbed CO associated with the Pd facets, but annealing these surfaces also shows a conversion to Pd(111) facets. LEED indicates that at coverages above 10 ML, the palladium particles exhibit (111) facets parallel to the substrate and aligned with the TiO2(110) unit cell, and that this ordering in the particles is enhanced by annealing. 相似文献
980.
Spin coating silica films were prepared from acid-catalyzed tetraethoxysilane (TEOS) solutions, and the magnitude of radiative striations formed on the surface of the resulting films was quantitatively evaluated by measuring surface roughness using a contact probe profilometer. Wave-like transverse profiles were obtained on the films prepared. Surface roughness parameters, Ra (arithmetical mean deviation), Rz (ten point height of irregularities) and S (mean spacing of local peaks), were determined. When the gel films were heated at higher temperatures (500°C), the film thickness decreased up to 22%, while none of Ra, Rz or S varied with heat-treatment temperature, indicating that the surface of the films is already densified at room temperature. Higher substrate rotation speeds caused decrease in Ra, Rz and S, revealing that the striations decreased both in amplitude and wavelength. Application of viscous sols aged for longer periods of time resulted in increased amplitude (Rz) of striations without change in wavelength (S). 相似文献