全文获取类型
收费全文 | 203989篇 |
免费 | 1966篇 |
国内免费 | 591篇 |
专业分类
化学 | 102384篇 |
晶体学 | 3340篇 |
力学 | 9294篇 |
综合类 | 5篇 |
数学 | 22478篇 |
物理学 | 69045篇 |
出版年
2021年 | 1655篇 |
2020年 | 1797篇 |
2019年 | 1998篇 |
2018年 | 2701篇 |
2017年 | 2601篇 |
2016年 | 3769篇 |
2015年 | 2310篇 |
2014年 | 3618篇 |
2013年 | 9087篇 |
2012年 | 7249篇 |
2011年 | 8740篇 |
2010年 | 6045篇 |
2009年 | 5910篇 |
2008年 | 7917篇 |
2007年 | 8083篇 |
2006年 | 7729篇 |
2005年 | 6895篇 |
2004年 | 6435篇 |
2003年 | 5655篇 |
2002年 | 5491篇 |
2001年 | 6424篇 |
2000年 | 4932篇 |
1999年 | 3795篇 |
1998年 | 3039篇 |
1997年 | 3045篇 |
1996年 | 2794篇 |
1995年 | 2613篇 |
1994年 | 2463篇 |
1993年 | 2339篇 |
1992年 | 2692篇 |
1991年 | 2672篇 |
1990年 | 2601篇 |
1989年 | 2399篇 |
1988年 | 2450篇 |
1987年 | 2448篇 |
1986年 | 2279篇 |
1985年 | 2968篇 |
1984年 | 3217篇 |
1983年 | 2635篇 |
1982年 | 2801篇 |
1981年 | 2771篇 |
1980年 | 2638篇 |
1979年 | 2727篇 |
1978年 | 2822篇 |
1977年 | 2819篇 |
1976年 | 2887篇 |
1975年 | 2674篇 |
1974年 | 2645篇 |
1973年 | 2779篇 |
1972年 | 1763篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
Two series of tensile relaxation tests are performed on natural rubber filled with high abrasion furnace black. To fit observations, constitutive equations are derived for the nonlinear viscoelastic behavior of a particle-reinforced elastomer. A filled rubber is modeled as a composite medium, where inclusions with low concentrations of junctions are randomly distributed in the host matrix. The inclusions are treated as equivalent networks of macromolecules, where strands can separate from temporary junctions as they are thermally agitated. The bulk medium is thought of as a permanent network of chains. Unlike conventional concepts of transient networks, the concentration of strands in inclusions is assumed to be affected by mechanical factors: under active loading, inter-chain interactions weaken and some strands that were prevented from detachment from their junctions in a stress-free compound become free to separate from the junctions in a deformed medium. Unloading strengthens interactions between macromolecules, which results in an increase in the number of permanent strands. By using the laws of thermodynamics, stress–strain relations for a particle-reinforced rubber are developed. Adjustable parameters in the constitutive equations are found by fitting the experimental data. It is demonstrated that mechanical pre-loading and annealing of specimens at an elevated temperature noticeably affect concentrations of inclusions with various activation energies for rearrangement of strands. 相似文献
972.
Transport in Porous Media - 相似文献
973.
S. Burachas S. Beloglovsky D. Elizarov I. Makov Yu. Saveliev N. Vassilieva M. Ippolitov V. Manko S. Nikulin A. Nyanin A. Vasiliev A. Apanasenko G. Tamulaitis 《Radiation measurements》2004,38(4-6):367-370
Technological conditions ensuring growth of optically homogeneous lead tungstate (PWO) crystals are reported. It is shown that the basic scintillator characteristics of PWO grown from highly purified raw material and properly doped with lanthanides are mainly determined by inclusions of oxides W1−yLyO3−x (L=Y, La, Gd; 0<x<0.3). Moreover, surface-located inclusions with structure close to tungstenite may also be of importance. It is demonstrated that the scintillation properties can be intentionally designed by varying the oxygen content in the inclusions x and the surface structure. The optimal value for x and the most favorable surface structure are achieved by proper thermal regimes and environment content during the crystal annealing. The results enabled low-cost fabrication of PWO scintillators with steady and reproducible characteristics acceptable for the CERN project ALICE and ensured production of PWO on an industrial scale by “North Crystals” company at a rate of 125–135 crystals per year from every growth apparatus. 相似文献
974.
Backscattered-particle production is studied by means of a detailed simulation of cascade processes in a dense medium. The energy dependence of the albedo and the spatial and angular distributions of various components of this flux are analyzed. 相似文献
975.
D. N. Makovetskii 《Technical Physics》2004,49(2):224-231
Two qualitatively different types of resonant destabilization of phonon stimulated emission (SE) are discovered in experiments where a 9-GHz multimode ruby laser is periodically modulated (the electromagnetic pump frequency is 23 GHz). In the case of deep pump modulation at low modulation frequencies (ω=70–200 Hz, where ωm is the modulation frequency), a fast random alternation of microwave phonon SE modes is observed. This destabilization range corresponds to relaxation resonance in optical lasers. Outside the relaxation resonance range (at ωm≈10 Hz), the other type of resonant destabilization of stationary phonon SE is observed. This destabilization shows up as very slow regular self-detunings of the microwave SE spectra. The period of such self-organized motions depends significantly on ωm and changes by several orders of magnitude when ωm varies within several percent. The second type of SE resonant destabilization is explained in terms of antiphase energy exchange between modes in a modulated phaser. 相似文献
976.
Voitsekhovskii A. V. Grigor'ev D. V. Korotaev A. G. Kokhanenko A. P. 《Russian Physics Journal》2004,47(7):764-772
The effects of wide- and narrow- variband layers on the charge-carrier concentration and mobility in the MBE-grown epitaxial CMT structures measured by the Hall-effect method are studied by numerical simulation. The dependence of the relative difference between the experimentally obtained effective values of electrophysical parameters and those of an epitaxial coating on the variband-layer characteristics is discussed. An analysis of this dependence shows that the manner in which the broad-band and narrow-band layers affect the resulting parameters is inequivalent. The calculations suggest that the effect of the wide-band layer on the experimental electrophysical parameters can be neglected. In the case of the narrow variband layer, however, the difference between the electophysical parameters strongly depends on the variband-layer parameters and the concentrations of ionized donor and acceptor centers. 相似文献
977.
978.
979.
Classification of three-dimensional periodic fluid flows 总被引:1,自引:0,他引:1
980.