全文获取类型
收费全文 | 747篇 |
免费 | 34篇 |
国内免费 | 51篇 |
专业分类
化学 | 236篇 |
晶体学 | 34篇 |
力学 | 109篇 |
数学 | 7篇 |
物理学 | 446篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 5篇 |
2021年 | 18篇 |
2020年 | 20篇 |
2019年 | 8篇 |
2018年 | 16篇 |
2017年 | 14篇 |
2016年 | 23篇 |
2015年 | 20篇 |
2014年 | 26篇 |
2013年 | 27篇 |
2012年 | 35篇 |
2011年 | 69篇 |
2010年 | 49篇 |
2009年 | 59篇 |
2008年 | 51篇 |
2007年 | 62篇 |
2006年 | 63篇 |
2005年 | 26篇 |
2004年 | 46篇 |
2003年 | 44篇 |
2002年 | 22篇 |
2001年 | 11篇 |
2000年 | 8篇 |
1999年 | 21篇 |
1998年 | 10篇 |
1997年 | 13篇 |
1996年 | 11篇 |
1995年 | 12篇 |
1994年 | 3篇 |
1993年 | 8篇 |
1992年 | 7篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1985年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有832条查询结果,搜索用时 15 毫秒
91.
Analytical and experimental investigations are performed in order to characterize the dynamic behaviour of a non-smooth rotational oscillator, which exhibits multiple discontinuity boundaries in the phase space. The physical system consists of a rotating body subjected to an elastic restoring force and in contact with one or two rough discs rotating with constant driving velocities. The presence of multiple discontinuity boundaries caused by frictional contacts leads to non-standard bifurcations that are studied by means of a simple mechanical model.A test set-up has then been built to investigate the correctness of modelling of the friction force and the validity of the proposed model for technical applications: the experimental measurements qualitatively and quantitatively capture the basic scenarios anticipated by the model while a strong robustness of the phenomena pointed out by the theoretical analyses has been revealed in the experiments. 相似文献
92.
93.
This paper presents a more detailed interaction of an electromagnetics light with a metallic surface-relief subwavelength grating utilizing the rigorous coupled-wave analysis. The focus of this work is the accurate modeling of undetermined aspects of diffraction patterns produced by binary metallic grating structures, specially gold grating. First-order diffraction efficiency for rectangular-groove gold grating with equal groove and ridge widths are presented for various wavelengths as a function of period, groove depth, polarization and angle of incidence. We also studied diffraction efficiency of both of TE and TM polarization modes against increasing of incident angle as well as TE polarization against increment of grating period. As a result, very low reflectivity at zero-order was found out for TE and TM polarizations at the pitch of Λ = 2λ. Having been studied diffraction efficiency of metallic surface-relief gratings, we also examined polarization-dependent efficiency of diffraction orders, for different groove depths. Simulation results have been completely presented. 相似文献
94.
95.
Epitaxy provides thin films in a perfect periodic structure. In heteroepitaxy the misfit may yield perfect pseudomorphic films or relaxed films, which may show the periodicities of the substrate and the film and their combinations. Then non-periodic defects like mosaics may appear, e.g., due to dislocations. Deviations from exact epitaxial positions in strictly periodic structures can be determined from diffraction intensities. For more complex surfaces, e.g., films with defects like mosaics or large superstructures or on substrates with steps such a strict determination is not possible. From the spot profile analysis of low energy electron diffraction (LEED) or X-ray data some structural information is available for these surfaces with defects. This new type of evaluation is demonstrated with spot profile analysis of LEED (SPA-LEED) for ultrathin Pb films on Si(1 1 1)7 × 7 surface, which grow even at 25 K epitaxially in a layer-by-layer growth mode. The analysis provides the first information on deviation from the exact epitaxial positions of the surface Pb atoms. A vertical shift of domains and an inclination between domains provides an explanation of the experimental results. 相似文献
96.
Thin films of the rare-earth metal Dy were grown on W(1 1 2) at room temperature and 570 K. Then the resultant film morphologies were characterised by LEED and STM. A series of novel film morphologies, including c(4 × 6), c(5 × 12) and (5 × 8) structures, were found that are unique among the rare-earth metals. High thermal stability was found for the Dy films (up to 1650 K, close to the melting point at 1685 K) such that the Dy atoms preserved an ordered structure and the Dy volatility was less than would be expected from its vapour pressure. This is an indication of strong electronic interactions between the Dy atoms and the W(1 1 2) substrate. 相似文献
97.
S. Caravati G.P. Brivio S. Pagliara G. Galimberti C. Giannetti 《Surface science》2006,600(18):3901-3905
Recent advances in both the experimental resolution and in the computational capabilities motivate new studies of surface properties. In particular, a detailed comparison between theoretical and experimental data is expected to provide a better insight into surface and image states. In this work we present a joint effort analyzing such features of the Cu(1 1 1) and Cu(0 0 1) surfaces. The experiments are performed by using both linear and non-linear angle-resolved photoemission. From the theoretical point of view, we make use of the Green function embedding technique within density functional theory. We are able to account for the image states by suitably modifying the effective potential in the Kohn-Sham equation and the generalized boundary conditions on the Green function. Comprehensive theoretical and experimental results on the effective mass and the binding energy of the Shockley state and the first image states are reported. 相似文献
98.
Z. Dohnálek 《Surface science》2006,600(17):3461-3471
Thin Pd films (1-10 monolayers, ML) were deposited at 35 K on a Pt(1 1 1) single crystal and on an oxygen-terminated FeO(1 1 1) monolayer supported on Pt(1 1 1). Low energy electron diffraction, Auger electron spectroscopy, and Kr and CO temperature programmed desorption techniques were used to investigate the annealing induced changes in the film surface morphology. For growth on Pt(1 1 1), the films order upon annealing to 500 K and form epitaxial Pd(1 1 1). Further annealing above 900 K results in Pd diffusion into the Pt(1 1 1) bulk and Pt-Pd alloy formation. Chemisorption of CO shows that even the first ordered monolayer of Pd on Pt(1 1 1) has adsorption properties identical to bulk Pd(1 1 1). Similar experiments conducted on FeO(1 1 1) indicate that 500 K annealing of a 10 ML thick Pd deposit also yields ordered Pd(1 1 1). In contrast, annealing of 1 and 3 ML thick Pd films did not result in formation of continuous Pd(1 1 1). We speculate that for these thinner films Pd diffuses underneath the FeO(1 1 1). 相似文献
99.
主要用第四周期金属元素的氧化物与Al2O3的复合氧化物催化剂上甲烷氧化的结果证实了催化剂设计中的预测:(1)催化剂首先应能解离活化甲烷,(2)催化剂要能较快地活化O2分子.只有同时满足这两个条件,催化剂才可能有较好的甲烷部分氧化活性.第四周期元素中只有镍具有这样的性质.Cu,Mn,Cr,La,Ca,Zn等氧化物的添加可明显提高Ni-Al2O3催化剂的甲烷部分氧化性能,其中Cu的助催化性能最好.催化剂NiO-CuO-Al2O3,NiO-MnO-Al2O3,NiO-Cr2O3-Al2O3的反应活性和选择性顺序,与金属Cu,Mn,Cr上CO和H2脱附的顺序是一致的 相似文献
100.
Dominic R. Alfonso 《Surface science》2006,600(19):4508-4516
Density functional theory is used to investigate the initial inclusion of sulfur into the subsurface interstitial sites of Pd(1 1 1) surface. Pure subsurface adsorption is found to be less energetically favorable than on-surface adsorption. The incorporation of sulfur into the metal becomes more favorable than continuous adsorption on the surface after a critical on-surface sulfur coverage. We find subsurface sulfur occupation to be energetically favorable after adsorption of more than half a monolayer on the surface. Occupation of subsurface sites induces a pronounced structural distortion of the Pd(1 1 1) surface. We find significant expansion of interplanar spacing between the uppermost surface metal layers and rearrangement of the S overlayer. The interplay between the energy cost due to structural distortion of Pd(1 1 1) and the energy gain due to bond formation for different structures is discussed. 相似文献