全文获取类型
收费全文 | 468344篇 |
免费 | 6677篇 |
国内免费 | 1238篇 |
专业分类
化学 | 252942篇 |
晶体学 | 6635篇 |
力学 | 19332篇 |
综合类 | 14篇 |
数学 | 57403篇 |
物理学 | 139933篇 |
出版年
2021年 | 4106篇 |
2020年 | 4707篇 |
2019年 | 4991篇 |
2018年 | 6596篇 |
2017年 | 6410篇 |
2016年 | 10119篇 |
2015年 | 6614篇 |
2014年 | 9523篇 |
2013年 | 22455篇 |
2012年 | 17687篇 |
2011年 | 21141篇 |
2010年 | 14771篇 |
2009年 | 14439篇 |
2008年 | 19310篇 |
2007年 | 19029篇 |
2006年 | 17581篇 |
2005年 | 15932篇 |
2004年 | 14667篇 |
2003年 | 12869篇 |
2002年 | 12523篇 |
2001年 | 13956篇 |
2000年 | 10651篇 |
1999年 | 8333篇 |
1998年 | 6908篇 |
1997年 | 6616篇 |
1996年 | 6483篇 |
1995年 | 5770篇 |
1994年 | 5767篇 |
1993年 | 5539篇 |
1992年 | 6192篇 |
1991年 | 6195篇 |
1990年 | 5968篇 |
1989年 | 5742篇 |
1988年 | 5746篇 |
1987年 | 5598篇 |
1986年 | 5317篇 |
1985年 | 6880篇 |
1984年 | 6985篇 |
1983年 | 5541篇 |
1982年 | 5631篇 |
1981年 | 5623篇 |
1980年 | 5163篇 |
1979年 | 5557篇 |
1978年 | 5684篇 |
1977年 | 5574篇 |
1976年 | 5536篇 |
1975年 | 5102篇 |
1974年 | 5060篇 |
1973年 | 5082篇 |
1972年 | 3567篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
M. N. Vidyakin Yu. N. Lazareva Yu. P. Yampolskii A. Yu. Alentiev D. Yu. Likhachev A. L. Rusanov O. V. Kozlova 《Polymer Science Series A》2006,48(6):596-600
The correlation between chemical structure and gas transport properties is considered for a new class of membrane materials based on structurally similar polyphenylquinoxalines that are characterized by different numbers of flexible-O-ether bonds in the repeating unit and different chain rigidities. Permeability, diffusion, and solubility coefficients have been estimated for the gases H2, He, O2, N2, CO, CO2, and CH4; separation factors for various gas pairs have been determined. For the materials with a similar level of cohesive energy density, which characterizes interchain interactions, permeability decreases with a decrease in chain rigidity, whereas selectivity of gas separation increases. 相似文献
992.
This study has investigated the effect of shelf aging, for up to one year in air, on the properties of gamma-irradiated ultra-high molecular weight polyethylene (UHMWPE). A variety of techniques were used to characterize the properties of treated samples. Differential scanning calorimetery (DSC) was used to characterize the morphology. The extent of cross-linking in a polymer network was detected by swelling measurements. The durometer hardness test was used to measure the relative hardness of this material, and changes in density were also measured. Results from all these measurements were combined to explain the changes in the microstructure of the aged, irradiated UHMWPE. This study shows that crystallinity is increased with radiation dose and with aging due to chain scission, which leads to a reduction in the molecular weight of the material. This allows the chains to rearrange to form crystalline regions. Positron annihilation lifetime spectroscopy confirms these conclusions. Fractional free volumes have been deduced from lifetime parameters, which correlate with the data obtained by the other techniques. 相似文献
993.
Present paper deals with the structural, magnetic and transport studies of as-deposited as well as annealed Co/GaAs(0 0 1) thin film at different temperatures. The X-ray diffraction measurements show oriented growth of as-deposited Co film in the hcp (0 0 2) direction. However, the sample annealed at higher temperatures shows formation of ternary Co2GaAs phase at the interface. Corresponding magnetic and transport measurements show decrement in magnetization and resistivity with annealing temperatures. The observed reductions in magnetization and resistivity values are mainly attributed to the formation of ternary Co2GaAs phase at the interface. 相似文献
994.
995.
J. Kh. Nurligareev K. M. Golant V. A. Sychugov B. A. Usievich 《Technical Physics》2006,51(8):1030-1034
The propagation of a pencil beam in a circuital system of tunnel-coupled waveguides is considered. It is shown that the beam periodically focuses into a point when moving along the trajectory. A maximal number of waveguides supporting the propagation of the beam can be estimated in simple terms. The cross-sectional area of the waveguides can be subdivided into three zone with the beam pulsing only in the central one. 相似文献
996.
O. M. Zhigalina K. A. Vorotilov A. S. Sigov A. S. Kumskov 《Physics of the Solid State》2006,48(6):1205-1207
Barium strontium titanate (BST) films on Si-SiO2-Ti-Pt substrates are prepared by chemical solution deposition upon crystallization on a sublayer. The structure of the BST films is investigated using transmission electron microscopy, high-resolution electron microscopy, and x-ray diffraction analysis. 相似文献
997.
E. D. Mishina N. É. Sherstyuk V. O. Val’dner A. V. Mishina K. A. Vorotilov V. A. Vasil’ev A. S. Sigov M. P. De Santo E. Cazzanelli R. Barberi Th. Rasing 《Physics of the Solid State》2006,48(6):1210-1213
Ferroelectric composite two-dimensional ferroelectric/aluminum oxide nanostructures were studied. A porous aluminum oxide matrix was used as a template into which a ferroelectric precursor was introduced, followed by annealing. The prepared nanostructures were studied using optical second harmonic generation and micro-Raman scattering. 相似文献
998.
Currents in high-resistivity semiconductors arising due to the rectification of space-charge waves are theoretically studied. Attention is primarily focused on the situation where the effective trap concentration is low. It is shown that, in this case, the dispersion law of trap-recharging waves changes from the inverse proportionality to a linear law and the drift waves no longer exist. In crystals with bipolar conduction, there are two modes of trap-recharging waves with a linear dispersion law. The dc and ac currents are found for the first time as functions of the trap concentration, the mobility and lifetime of carriers, the wavenumber of space-charge waves, and the applied electric field. 相似文献
999.
L. I. Bryukvina E. A. Ermolaeva S. N. Pidgurskiĭ L. F. Suvorova V. M. Khulugurov 《Physics of the Solid State》2006,48(1):68-72
It was detected for the first time that films consisting of a transition-metal-based structure form (via thermal diffusion
of intracrystalline impurities) on the surface of alkali-halide (LiF, NaF) crystals activated by transition metals Co, Ni,
or Mn. The thickness, density, and composition of the films are shown to be different, depending on the heat treatment conditions.
The crystals were annealed at temperatures varying from 473 to 1073 K in vacuum and air. The surface structures forming upon
annealing in vacuum exhibit magnetic properties. The films were studied by optical, x-ray fluorescence, and electron spectroscopy
to reveal the mechanisms of transition-metal film formation during thermal annealing. 相似文献
1000.
The direct growth of ZnSe–CdSe solid solution onto metallic cathodes by electrodeposition from acidic aqueous sulphate solutions
is described. The plating process is studied by simple voltammetry, while the structure and composition of the electrolytic
deposits are investigated by X-ray diffraction. The experimental d-spacing values of the as-grown mixed lattice are compared to data from reference Zn
x
Cd1-x
Se pellets of standard composition, produced by a sintering method. The findings are supplemented with energy-dispersive X-ray
(EDX) elemental analysis. Thereupon, the variation of the mole fraction x in Zn
x
Cd1-x
Se, and the solid phase constitution of the electrodeposits are determined and correlated to the electrochemical conditions
of growth. The resulting films contain admixtures of CdSe compound and metallic Cd. 相似文献