全文获取类型
收费全文 | 84814篇 |
免费 | 570篇 |
国内免费 | 130篇 |
专业分类
化学 | 41262篇 |
晶体学 | 1260篇 |
力学 | 3277篇 |
综合类 | 1篇 |
数学 | 7827篇 |
物理学 | 24686篇 |
无线电 | 7201篇 |
出版年
2022年 | 656篇 |
2021年 | 926篇 |
2020年 | 1054篇 |
2019年 | 1194篇 |
2018年 | 1703篇 |
2017年 | 1799篇 |
2016年 | 2282篇 |
2015年 | 1063篇 |
2014年 | 1840篇 |
2013年 | 3462篇 |
2012年 | 3040篇 |
2011年 | 3427篇 |
2010年 | 2814篇 |
2009年 | 2909篇 |
2008年 | 3304篇 |
2007年 | 3263篇 |
2006年 | 3084篇 |
2005年 | 2772篇 |
2004年 | 2544篇 |
2003年 | 2398篇 |
2002年 | 2397篇 |
2001年 | 2500篇 |
2000年 | 1893篇 |
1999年 | 1494篇 |
1998年 | 1368篇 |
1997年 | 1249篇 |
1996年 | 1068篇 |
1995年 | 988篇 |
1994年 | 968篇 |
1993年 | 942篇 |
1992年 | 986篇 |
1991年 | 1065篇 |
1990年 | 1017篇 |
1989年 | 1011篇 |
1988年 | 917篇 |
1987年 | 828篇 |
1986年 | 801篇 |
1985年 | 942篇 |
1984年 | 1014篇 |
1983年 | 860篇 |
1982年 | 878篇 |
1981年 | 777篇 |
1980年 | 729篇 |
1979年 | 797篇 |
1978年 | 914篇 |
1977年 | 945篇 |
1976年 | 834篇 |
1975年 | 798篇 |
1974年 | 817篇 |
1973年 | 788篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
O. I. Berngardt 《Radiophysics and Quantum Electronics》2006,49(6):415-431
We propose a model of coherent-echo signals during the monostatic sounding of the ionosphere. The model is based on the previously
obtained radar equation for separate samples of the scattered signal. The dielectric-permittivity perturbation described by
a discrete set of spatial harmonics modulated in space and time is used as the scattering irregularities. The model was tested
using Irkutsk incoherent-scatter radar data obtained during the coherent-echo observations in July 15 and 16, 2000. The test
shows that the model is suitable for describing the observed characteristics of separate sample spectra of the coherent-echo
signals.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 6, pp. 459–477, June 2006. 相似文献
22.
23.
O. N. Kozakov 《Optics and Spectroscopy》2002,93(4):598-602
A method of calculating the partial characteristics of radiation absorption by the components of light-scattering disperse layers is proposed. This method is based on statistical modeling (the Monte Carlo method). The absorptivities of photographic gelatin and silver bromide microcrystals and the corresponding distributions of the absorbed energy over the layer thickness are calculated using the example of an interaction between actinic radiation and silver halide photographic layers in the wavelength range λ=200–440 nm. The following structural parameters of the photographic layer are used in the calculation: the mean size of emulsion crystals d=0.5 μm; the polydispersity C V =25%; the volume concentrations C V =10, 20, and 30%; and the thickness of the emulsion layer H=10 μm. 相似文献
24.
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
25.
26.
O. Ya. Savchenko 《Optics and Spectroscopy》2006,101(2):179-182
The efficiency with which a magnetic field acts on sublevels of the first and second doublets of a hydrogen-like atom is shown to vary because of relativistic effects by a factor of 1 ? 2γ(l + 1)/(2l + 3) and 1 ? 2γl/(2l ? 1), respectively, where γ is the ratio of the electron binding energy to the rest energy and l is the quantum number of the orbital angular momentum. 相似文献
27.
A new speckle shearing interferometer with simple setup is proposed. The interferometer can be converted easily from a speckle referenced speckle pattern interferometer into a speckle shearing interferometer and vice versa. A beamsplitter and a mirror are used to generate the shear. The amount of shear can be adjusted by simply rotating the mirror. The costs involved are low and it is particularly useful for fast inspection in non-destructive testing of structural integrity. Both the theoretical studies of the method of measurement and the experimental results are presented. 相似文献
28.
K. E. Mochalov O. A. Ustinova S. A. Strel’tsov S. L. Grokhovskii A. L. Zhuze I. R. Nabiev A. V. Sukhanova V. A. Oleinikov 《Optics and Spectroscopy》2002,93(4):493-500
Topotecan (TPT), a water-soluble derivative of camptothecin (inhibitor of human DNA topoiomerase I), has found wide application in cancer chemotherapy. The central problem in using topotecan is the presence of lactone rings in its molecules, which undergo hydrolysis at a physiological pH yielding an inactive and even toxic form of the drug. The analysis of Raman spectra of TPT in H2O and D2O solutions made it possible to assign the spectral bands to the vibrations of particular molecular groups. Spectral features indicative of the opening of the lactone rings of the TPT molecules, deprotonation of the hydroxyl groups in their quinoline fragments, and of possible participation of the hydroxyl and carbonyl groups in H bonding are found. The data obtained are necessary to study the molecular mechanisms of TPT-DNA interaction and the formation of ternary complexes between TPT, DNA, and DNA topoisomerase I. 相似文献
29.
The existence of linear nonstationary optical resonances in a diatomic nanostructural object with a dipole-dipole atomic interaction has been proved. A new solution to the joint system of modified Bloch optical equations and nonlocal field equations is obtained for time intervals much shorter than the times of phase and energy relaxation. Formulas for effective polarizabilities of the object’s atoms, which have a set of dimensional resonances, are derived. The frequencies of these resonances significantly differ from the eigenfrequencies of the object’s atoms, and their properties depend on the interatomic distance, light-pulse duration, initial atomic inversions, and the orientation of the object’s axis relative to the direction of incidence of the external light wave. 相似文献
30.
We use the adiabatic hyperspheric expansion and the Faddeev decomposition of the wave function with only s-waves. We derive for a fixed hyperradius an integro-differential equation for the angular eigenvalue and wave function. The
correlations lower the interaction energy for N = 20 by about a factor of 5.
Received October 22, 2001; accepted for publication November 5, 2001 相似文献