全文获取类型
收费全文 | 4635篇 |
免费 | 178篇 |
国内免费 | 29篇 |
专业分类
化学 | 2557篇 |
晶体学 | 51篇 |
力学 | 181篇 |
数学 | 1140篇 |
物理学 | 913篇 |
出版年
2023年 | 40篇 |
2022年 | 104篇 |
2021年 | 137篇 |
2020年 | 127篇 |
2019年 | 157篇 |
2018年 | 155篇 |
2017年 | 144篇 |
2016年 | 194篇 |
2015年 | 151篇 |
2014年 | 205篇 |
2013年 | 338篇 |
2012年 | 309篇 |
2011年 | 324篇 |
2010年 | 178篇 |
2009年 | 197篇 |
2008年 | 237篇 |
2007年 | 205篇 |
2006年 | 156篇 |
2005年 | 126篇 |
2004年 | 129篇 |
2003年 | 95篇 |
2002年 | 89篇 |
2001年 | 79篇 |
2000年 | 65篇 |
1999年 | 45篇 |
1998年 | 33篇 |
1997年 | 38篇 |
1996年 | 57篇 |
1995年 | 45篇 |
1994年 | 43篇 |
1993年 | 48篇 |
1992年 | 40篇 |
1991年 | 37篇 |
1990年 | 31篇 |
1989年 | 24篇 |
1988年 | 29篇 |
1987年 | 40篇 |
1986年 | 39篇 |
1985年 | 36篇 |
1984年 | 27篇 |
1983年 | 25篇 |
1982年 | 32篇 |
1981年 | 29篇 |
1980年 | 22篇 |
1979年 | 37篇 |
1978年 | 28篇 |
1977年 | 21篇 |
1976年 | 23篇 |
1975年 | 20篇 |
1974年 | 14篇 |
排序方式: 共有4842条查询结果,搜索用时 31 毫秒
991.
992.
Nguyen Ngoc Chan 《Czechoslovak Journal of Physics》1988,38(6):666-671
Using the method of double-time retarded Green function, an expression for the spin energy spectrum including the contributions of one-phonon and two-phonon processes has been derived. Calculations have been performed using the spin wave approximation. The broadening of the energy level is roughly estimated in a peculiar case.I would like to thank Dr. Dagmat Fraitová for her advice and help. 相似文献
993.
Nguyen Ba Chanh Christian Hauw Alain Meresse Madeleine Rey-Lafon Laure Ricard 《Journal of Physics and Chemistry of Solids》1985,46(12):1413-1420
The existence of three main crystalline phases (called III, II and I) in (C12H25NH3)2CdCl4 has been revealed by differential scanning calorimetry. X-ray diffraction and spectroscopic studies. The crystal- lographic evolution with increasing temperature appears to be monoclinic (III) → orthorhombic (II) → tetragonal (I). The low temperature phase III is the only ordered structure. The phase transition (III-II), which is of first order type, corresponds to an order-disorder mechanism involving the organic part of the structure (alkylammonium chains) whereas the phase transition (II-I), which is of second-order type, is related to the arrangement of the mineral matrix (octahedra of perovskite layers). An intermediate disordered form II', stable in a very narrow temperature range and structurally similar to the form II, has also been observed, so that the transformation (III-II) proceeds, in fact, in two steps (III-II'-II). The variation enthalpies observed at the transitions (III-II'-II) and analyzed through an order-disorder mechanism demonstrate the high disorder of the alkylammonium chains in form II, in agreement with spectroscopic results. No thermal anomaly or spectroscopic modification is observed for the high temperature transition (II-I). 相似文献
994.
X-ray photoelectron spectroscopy (XPS) technique have been used to investigate the interface formed between poly(2-methoxy-5-(2′-ethyl-hexyloxyl)-p-phenylene vinylene) (MEH-PPV) and indium tin oxide (ITO) layer in top emission organic light emitting diodes. A weak but noticeable diffusion of indium into the polymer film was observed. Interactions between the diffused metallic atoms with the polymer resulted in the formation of carbon-metal complexes at the interface region. Compared to the ITO/MEH-PPV interface, the penetration of indium into the polymer layer was less important and may be explained by the surface morphology of the polymer film. It was however, a probable factor for fast degradation of devices using this structure. 相似文献
995.
Anh-Tuan Le Chong-Oh Kim Nguyen Chau Nguyen Duy Cuong Nguyen Duc Tho Nguyen Quang Hoa Heebok Lee 《Journal of magnetism and magnetic materials》2006
In this paper, the effect of microstructural and surface morphological developments on the soft magnetic properties and giant magneto-impedance (GMI) effect of Fe73.5−xCrxSi13.5B9Nb3Au1 (x=1, 2, 3, 4, 5) alloys was investigated. It was found that the Cr addition causes slight decrease in the mean grain size of α-Fe(Si) grains. AFM results indicated a large variation of surface morphology of density and size of protrusions along the ribbon plane due to structural changes caused by thermal treatments with increasing Cr content. Ultrasoft magnetic properties such as the increase of magnetic permeability and the decrease of coercivity were observed in the samples annealed at 540 °C for 30 min. Accordingly, the GMI effect was also observed in the annealed samples. 相似文献
996.
O.G. Kosareva T. Nguyen W. Liu V.P. Kandidov M. Scalora S.L. Chin 《Optics Communications》2006,267(2):511-523
We have shown experimentally and confirmed by means of full dimensional (3D + 1) numerical simulations, the possibility to create an array of refractive index modification zones inside a fused silica sample using a 43 fs, 2 mJ, 800 nm laser pulse and a periodic mesh introduced in front of the sample. Robust filaments and the corresponding refractive index modification zones preserve their transverse positions for more than 10 Rayleigh lengths (∼500 μm). Numerical simulations prove that each mesh unit is an independent source of the background energy for a filament formed within this unit. The effect of the simultaneous formation of many extended periodically spaced filaments can be used to accelerate the fabrication of microoptics devices. 相似文献
997.
In this paper we give sufficient spectral conditions for the almost automorphy of bounded solutions to differential equations with piecewise constant argument of the form x′(t)=Ax([t])+f(t), t∈R, where A is a bounded linear operator in X and f is an X-valued almost automorphic function. 相似文献
998.
A rather complete work on transition-metal (TM)-doped TiO2 thin films has been done and room ferromagnetism (FM) is found in the whole series of Sc/V/Cr/Mn/Fe/Co/Ni-doped TiO2 films. Not only is it remarkable that for the first time, FM at high temperature was achieved in TM-doped TiO2, but also a very big magnetic moment of 4.2μB/atom could be obtained, and direct evidences of real ferromagnets with big domains were shown as well. A similar chemical trend was achieved in TM-doped In2O3 films, however, the observed magnetic moment is rather modest, with the maximal value is of only 0.7μB/atom for Ni-doped In2O3 films. As regards TM-doped SnO2 films, observed magnetic moments could be very large, with the maximum saturation of 6μB per impurity atom for Cr-doped SnO2 thin films, but it could be influenced very much depending on substrate types. On the other hand, results on TM-doped ZnO films interestingly have revealed that in these systems, the magnetism more likely resulted from defects and/or oxygen vacancies. 相似文献
999.
An oriented dendrite-like texture is reported, appearing at a definite temperature in the nematic phase range of 4-n-heptyl- and 4-n-octyl-oxybenzoic acids (HOBA and OOBA), aligned by rubbed polyimide and preceding the smectic C phase, on cooling. Two preferred directions with respect to the 'easy' axis are indicated in the dendrites grown of HOBA and OOBA. We discuss a possible mechanism, at molecular and supramolecular levels, for this dendrite growth; and assume that the building 'blocks' of the dendrites are oligomers, or mixture of oligomers with 'free' closed and open dimers, constituting a detached crystalline layered state (named by us SmX, a smectic state intermediate between the N1 ordinary nematic and SmC phases). The study of the dynamics of the dendrite growth demonstrates a scaling relationship typical for non-equilibrium systems. The observed dendrites can be considered as patterns formed in complex non-linear dissipative systems, driven outside of equilibrium. 相似文献
1000.
Nguyen Minh Tri 《Mathematical Notes》1996,63(1):84-93
The paper deals with nonlinear problems for equations of Grushin type. We prove some nonexistence results via Pokhozhaev’s identity. In the rest of the paper we prove some results on smoothness near the boundary of eigenfunctions by using an explicit formula for fundamental solutions and the Kelvin transform for the operator. 相似文献