全文获取类型
收费全文 | 621879篇 |
免费 | 5207篇 |
国内免费 | 1662篇 |
专业分类
化学 | 320926篇 |
晶体学 | 9177篇 |
力学 | 29930篇 |
综合类 | 22篇 |
数学 | 78335篇 |
物理学 | 190358篇 |
出版年
2021年 | 5422篇 |
2020年 | 5970篇 |
2019年 | 6658篇 |
2018年 | 8866篇 |
2017年 | 8964篇 |
2016年 | 12546篇 |
2015年 | 6908篇 |
2014年 | 11429篇 |
2013年 | 27176篇 |
2012年 | 20828篇 |
2011年 | 24963篇 |
2010年 | 18475篇 |
2009年 | 18157篇 |
2008年 | 23482篇 |
2007年 | 23335篇 |
2006年 | 21475篇 |
2005年 | 19428篇 |
2004年 | 17954篇 |
2003年 | 16179篇 |
2002年 | 16028篇 |
2001年 | 17086篇 |
2000年 | 13272篇 |
1999年 | 10273篇 |
1998年 | 8962篇 |
1997年 | 8832篇 |
1996年 | 8246篇 |
1995年 | 7548篇 |
1994年 | 7436篇 |
1993年 | 7153篇 |
1992年 | 7683篇 |
1991年 | 8139篇 |
1990年 | 7792篇 |
1989年 | 7732篇 |
1988年 | 7600篇 |
1987年 | 7393篇 |
1986年 | 7051篇 |
1985年 | 9075篇 |
1984年 | 9513篇 |
1983年 | 8000篇 |
1982年 | 8501篇 |
1981年 | 7897篇 |
1980年 | 7622篇 |
1979年 | 8082篇 |
1978年 | 8488篇 |
1977年 | 8298篇 |
1976年 | 8260篇 |
1975年 | 7885篇 |
1974年 | 7617篇 |
1973年 | 8098篇 |
1972年 | 5742篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
D.W. Mueller JrA.L. Crosbie 《Journal of Quantitative Spectroscopy & Radiative Transfer》2002,74(1):43-68
Three-dimensional radiative transfer in an anisotropic scattering medium exposed to spatially varying, collimated radiation is studied. The generalized reflection function for a semi-infinite medium with a very general scattering phase function is the focus of this investigation. An integral transform is used to reduce the three-dimensional transport equation to a one-dimensional form, and a modified Ambarzumian's method is applied to formulate a nonlinear integral equation for the generalized reflection function. The integration is over both the polar and azimuthal angles; hence, the integral equation is said to be in the double-integral form. The double-integral, reflection function formulation can handle a variety of anisotropic phase functions and does not require an expansion of the phase function in a Legendre polynomial series. Complicated kernel transformations of previous single-integral studies are eliminated. Single and double scattering approximations are developed. Numerical results are presented for a Rayleigh phase function to illustrate the computational characteristics of the method and are compared to results obtained with the single-integral method. Agreement between the two approaches is excellent; however, as the transform variable increases beyond five the number of quadrature points required for the double-integral method to produce accurate solutions significantly increases. A new interpolation scheme produces accurate results when the transform variable is large. 相似文献
132.
A comprehensive study of the long pulse Nd:YAG laser drilling of multi-layer carbon fibre composites 总被引:2,自引:0,他引:2
W. S. O. Rodden S. S. Kudesia D. P. Hand J. D. C. Jones 《Optics Communications》2002,210(3-6):319-328
The results of an extensive experimental study of the free running Nd:YAG laser drilling of a multi-layer carbon fibre composite, where adjacent layers have differently orientated fibres, are reported. For holes drilled with the laser operating in fixed-Q mode at 1064 nm, parallel sections of blind holes illustrating discontinuities in the hole size along a given section direction will be shown to occur at the interface between adjacent layers. An explanation for this effect is proposed. Detailed single pulse drilling characteristics will be presented illustrating the exit hole diameter as a function of pulse energy and material thickness. These characteristics illustrate a ‘stable' drilling regime in which the exit hole diameters are least sensitive to changes in pulse energy or material thickness and a less ‘stable' regime in which they are more strongly dependent on these parameters. Drilling characteristics will be given for two different beam qualities, illustrating the greater drilling depth and reduced hole size achievable with an improved beam quality. Finally holes drilled through a 2 mm thick sample of material with multiple pulses are considered. Size distribution curves for entrance and exit holes will be presented. The total energy required (number of pulses × pulse energy) to drill through 2 mm thick material will be reported as a function of pulse energy in stationary air and argon atmospheres and in a partial vacuum, illustrating a threshold energy which is dependent upon the drilling atmosphere. The threshold energies will be discussed with reference to plasma formation and the reactivity of the drilling atmosphere. 相似文献
133.
A.N Bekrenev 《Journal of Physics and Chemistry of Solids》2002,63(9):1627-1631
An unusually high mobility of atoms under intensive impulse reactions is explained by the behavior of point defects at the shock wave front. It is shown that either a shock wave front or moving dislocations can capture the interstitials, or they can be thermally activated in the direction of the shock wave propagation. 相似文献
134.
A. Bozkurt 《Journal of Physics and Chemistry of Solids》2002,63(4):685-690
Ionic conductivity of dry quaternary ammonium polymer, polydiallyldimethylammonium with Cl− and H2PO4− counter ions was studied in a wide range of frequencies (10−2-107 Hz) and temperatures (300-470 K). The data were analysed within the formalism of permittivity. WAXS, and thermal properties of this polymer were investigated prior to conductivity measurements. 相似文献
135.
A. E. Angervaks S. A. Dimakov S. I. Kliment’ev A. I. Ryskin A. S. Shcheulin 《Optics and Spectroscopy》2002,93(2):307-314
The diffraction efficiency and the recording and relaxation times of dynamic reflection holograms, recorded in CdF2 crystals with bistable centers are studied experimentally in the temperature range 20–100°C. In the model experiments which measured the quality of the wave reflected from the hologram, the dynamic wavefront distortions are demonstrated to be efficiently compensated using a holographic corrector based on these crystals. CdF2 crystals with bistable centers are likely to be useful in solving problems of correction of laser light wavefront and image correction in observation telescopes with nonideal primary mirrors. 相似文献
136.
A. V. Ponosov 《Journal of Mathematical Sciences》1991,56(3):2492-2496
We study properties of some linear and nonlinear operators which occur in the theory of stochastic differential and integral equations.Translated from Statisticheskie Metody Otsenivaniya i Proverki Gipotez, pp. 148–154, 1988. 相似文献
137.
A. I. Bril' V. P. Kabashnikov N. V. Kuz'mina Yu. V. Khodyko 《Journal of Applied Spectroscopy》1991,55(3):934-939
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 3, pp. 478–484, September, 1991. 相似文献
138.
A fast-frequency modulated (FM) diode laser has been optically narrowed using the technique of resonant optical feedback, to provide linewidths in each FM mode of ≈ 200 kHz peak-to-peak. With a drive frequency of 50 MHz and modulation index of 0.2, the FM laser has been used for the first time to obtain Doppler-free FM spectra of the Rb D1 line at 795 nm. The potential use of this system for laser frequency stabilisation is discussed. 相似文献
139.
A. P. Prudnikov Yu. A. Brychkov O. I. Marichev 《Journal of Mathematical Sciences》1991,54(6):1239-1341
Translated from Itogi Nauki i Tekhniki, Seriya Matematicheskii Analiz, Vol. 27, pp. 3–146, 1989. 相似文献
140.
V. K. Malyutenko A. I. Liptuga V. A. Botte V. I. Chernyakhovskii 《Journal of Applied Spectroscopy》1991,55(4):1024-1028
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 4, pp. 624–629, October, 1991. 相似文献