全文获取类型
收费全文 | 22952篇 |
免费 | 828篇 |
国内免费 | 63篇 |
专业分类
化学 | 14775篇 |
晶体学 | 377篇 |
力学 | 713篇 |
综合类 | 1篇 |
数学 | 1774篇 |
物理学 | 6203篇 |
出版年
2023年 | 236篇 |
2022年 | 571篇 |
2021年 | 525篇 |
2020年 | 588篇 |
2019年 | 708篇 |
2018年 | 641篇 |
2017年 | 627篇 |
2016年 | 917篇 |
2015年 | 638篇 |
2014年 | 1050篇 |
2013年 | 1906篇 |
2012年 | 1544篇 |
2011年 | 1684篇 |
2010年 | 1095篇 |
2009年 | 925篇 |
2008年 | 1105篇 |
2007年 | 1090篇 |
2006年 | 853篇 |
2005年 | 744篇 |
2004年 | 589篇 |
2003年 | 462篇 |
2002年 | 416篇 |
2001年 | 251篇 |
2000年 | 241篇 |
1999年 | 181篇 |
1998年 | 123篇 |
1997年 | 150篇 |
1996年 | 177篇 |
1995年 | 170篇 |
1994年 | 162篇 |
1993年 | 180篇 |
1992年 | 215篇 |
1991年 | 157篇 |
1990年 | 146篇 |
1989年 | 160篇 |
1988年 | 135篇 |
1987年 | 134篇 |
1986年 | 115篇 |
1985年 | 165篇 |
1984年 | 181篇 |
1983年 | 134篇 |
1982年 | 143篇 |
1981年 | 132篇 |
1980年 | 143篇 |
1979年 | 146篇 |
1978年 | 148篇 |
1977年 | 133篇 |
1976年 | 96篇 |
1975年 | 92篇 |
1974年 | 91篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Justina Grabowska Karuna Kar Nanda R.T. Rajendra Kumar J.P. Mosnier M.O. Henry Simon B. Newcomb Patrick McNally Lisa OReilly Xu Lu Enda McGlynn 《Superlattices and Microstructures》2007,42(1-6):327
Self-organized ZnAl2O4 nanostructures with the appearance (in SEM) of high aspect ratio horizontal nanowires are grown on uncatalysed c-sapphire by vapour phase transport. The nanostructures grow as three equivalent crystallographic variants on c-sapphire. Raman and cathodoluminescence spectroscopy confirm that the nanostructures are not ZnO and TEM shows that they are the cubic spinel, zinc aluminate, ZnAl2O4, formed by the reaction of Zn and O with the sapphire substrate. 相似文献
82.
Alignment of photon-induced L3 vacancies is studied in rare earth and highZ elements at energies of experimental interest, near thresholds to 60 keV, under nonrelativistic dipole approximation. Numerical
calculations of the matrix element are undertaken to produce theoretical data for comparison with the experimental findings.
The A2 values being s>0.1 at photoelectron energies <20 keV are certainly higher than 5–8% uncertainties quoted in experimental
results. Present findings are from a very basic model, hydrogen-like and can further be treated as reference to observe the
impact of screening, relativistic, multipole and retardation corrections to the model 相似文献
83.
Two binary mixtures of polar liquid crystal materials were previously reported to exhibit three incommensurate smectic A phases predicted for such materials on the basis of phenomenological theory. Results of our recent high-resolution X-ray scattering experiments show that no incommensurate phases exist in the two systems. Wide coexistence regions are found at first order transitions between various frustrated smectic phases of these mixtures. These regions were previously identified as the incommensurate smectic A phases. The phase diagrams of the two systems determined with high-resolution X-ray technique are shown to be in excellent agreement with Baroisa-Prost-Lubensky theory. 相似文献
84.
85.
S. C. Joshi M. P. Singh V. P. Pandey B. S. Rajput 《International Journal of Theoretical Physics》2002,41(6):1107-1125
In four-dimensional N = 4 supersymmetric gauge theory, we obtain an exact metric on the moduli space of quantum vacua and analyze the spectra of BPS states in weak as well as in strong coupling regions. Identifying the hypermultiplet of the dyonic state as a string stretched between D3-brane probe and a 7-brane, we demonstrate that the two hypermultiplets, which become massless at two singularities in supersymmetric theory, correspond to open strings beginning on the D3-brane and ending on the respective 7-brane. 相似文献
86.
D. M. Bhardwaj D. C. Jain S. Dalela Ravi Kumar N. L. Saini K. B. Garg 《Physica B: Condensed Matter》2004,350(4):366-374
We have made the XAFS measurements at the Cr–K-edge on natural Indian ruby single crystals (corundum) and its two irradiated samples with fluence 1×1012 Ni6+ and 5×1012 Ni6+ ions/cm2. Irradiated samples show interesting changes in their physical appearance. XANES measurements show progressive decrease in Δoct value on increase of Ni fluence in irradiated samples. EXAFS measurements on these samples show decrease in Cr–O distance on increase of Ni fluence. Lowering of Δoct value is correlated with the increase of Cr–O distance. 相似文献
87.
R.A. Gunasekaran M. Agarwal A. Singh P. Dubasi P. Coane K. Varahramyan 《Optics and Lasers in Engineering》2005,43(6):1086
A novel small fluid controlled optical lens system that is capable of displaying dynamic variation of its focal length and field-of-view (FOV) is designed and fabricated. In this active lens system, appropriate volume of the optical fluid can be pumped into or out of the lens chamber to provide double-convex (DCX) or double-concave (DCV) lens effect. Simple optical imaging experiments were performed using different sets of glass lenses with fixed focal lengths to determine the optimum lens configuration required for designing a dynamic optical lens system. The experimental results obtained from the glass lenses demonstrate that a combination of a single DCX lens with three DCV lenses provides a wider FOV. The flexible membranes for fluid controlled lenses were fabricated using polydimethylsiloxane polymer material, which has good optical transparency and elasticity. A simple fluid injection system is used to vary the radius of curvature of the lenses, and thereby to change the focal length. A dynamic optical lens system with a combination of one DCX and multiple variable focal length DCV lenses as designed here can image an object with a wide range of focal length and FOV. With this fluid controlled optical system, the FOV and focal length could be continuously varied and a maximum FOV of 118.3° could be achieved. The smallest f-number (f/#) for this fluid controlled single lens system was found to be 1.3, which corresponds to the numerical aperture value of 0.35. 相似文献
88.
89.
We have calculated total and differential cross-sections for 1s →ns (n = 2, 3, 4) electron impact excitation of hydrogen and hydrogenic ions at various energies in Coulomb-projected Born approximation.
Distortion due to static interactions, target polarization and exchange effects has been incorporated in the initial channel.
The present calculations have been compared with other theoretical and experimental results. 相似文献
90.
Conductivity, viscosity, turbidity, and NMR measurements were performed over most of the mole fraction range for sodium deoxycholate (SDC) with hexadecyltrimethylammonium bromide (HTAB), hexadecylpyridinium bromide (HPyBr), and hexadecylpyridinium chloride (HPyCl). All studies demonstrate that the mixed-micelle formation is more favorable in SDC plus HTAB rather than SDC plus HPyBr or SDC plus HPyCl mixtures. The results showed that the bulky pyridinium head groups of HPyBr or HPyCl create steric incompatibility with rigid SDC monomers in the mixed state. 相似文献