全文获取类型
收费全文 | 467432篇 |
免费 | 3948篇 |
国内免费 | 1643篇 |
专业分类
化学 | 230798篇 |
晶体学 | 6920篇 |
力学 | 23997篇 |
综合类 | 63篇 |
数学 | 63503篇 |
物理学 | 147742篇 |
出版年
2021年 | 4214篇 |
2020年 | 4699篇 |
2019年 | 5456篇 |
2018年 | 7731篇 |
2017年 | 7902篇 |
2016年 | 10377篇 |
2015年 | 5401篇 |
2014年 | 9405篇 |
2013年 | 19160篇 |
2012年 | 16107篇 |
2011年 | 19269篇 |
2010年 | 14918篇 |
2009年 | 14910篇 |
2008年 | 18267篇 |
2007年 | 18105篇 |
2006年 | 16580篇 |
2005年 | 14716篇 |
2004年 | 13694篇 |
2003年 | 12428篇 |
2002年 | 12569篇 |
2001年 | 12932篇 |
2000年 | 10047篇 |
1999年 | 7400篇 |
1998年 | 6617篇 |
1997年 | 6485篇 |
1996年 | 6100篇 |
1995年 | 5358篇 |
1994年 | 5519篇 |
1993年 | 5405篇 |
1992年 | 5651篇 |
1991年 | 6014篇 |
1990年 | 5813篇 |
1989年 | 5726篇 |
1988年 | 5470篇 |
1987年 | 5412篇 |
1986年 | 5185篇 |
1985年 | 6453篇 |
1984年 | 6706篇 |
1983年 | 5677篇 |
1982年 | 6022篇 |
1981年 | 5588篇 |
1980年 | 5161篇 |
1979年 | 5775篇 |
1978年 | 5977篇 |
1977年 | 6147篇 |
1976年 | 6268篇 |
1975年 | 5804篇 |
1974年 | 5742篇 |
1973年 | 5950篇 |
1972年 | 4829篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
M. U. Belyi V. V. Grabovskii S. E. Zelenskii B. A. Okhrimenko 《Journal of Applied Spectroscopy》1991,54(2):137-141
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 2, pp. 229–233, February, 1991. 相似文献
972.
973.
V. M. Kuz’kin O. Yu. Lavrova S. A. Pereselkov V. G. Petnikov K. D. Sabinin 《Acoustical Physics》2006,52(1):65-76
The space-time spectral characteristics of the field of background internal waves (IW) are obtained for two oceanic shelf
regions (the Atlantic shelf of the United States and the Kamchatka shelf) and analyzed. Within the framework of a numerical
experiment, it is shown that the observed anisotropy of the IW field may considerably affect the low-frequency sound fluctuations
in the aforementioned regions and, in particular, may change the interference invariant of the sound field. 相似文献
974.
975.
Using a density-functional method that employs linear combinations of atomic orbitals as basis sets, nonlocal norm-conserving pseudopotentials and the generalized gradient approximation for exchange and correlation, we found that at 0 K the atoms of an Fe monolayer on the Ni (111) surface occupy hcp rather than fcc sites, in keeping with previous predictions made using the ab initio all-electron full-potential linearized augmented plane wave method with the local spin density approximation. 相似文献
976.
Some additional conditions of applicability of the ergodic hypothesis to fiber ring interferometers (FRIs) with a loop consisting of a single-mode optical fiber (SMOF) with random inhomogeneities are considered. It is shown by mathematical modeling that the change in the phase difference of counterpropagating waves at the FRI output with the SMOF temperature is not a stationary random process. However, in a fairly narrow temperature range, this dependence can be assumed to be locally stationary. The conditions determining this temperature range are formulated. It is shown for a fairly large ensemble of independent realizations of random inhomogeneities in an SMOF that, even when all conditions of ergodicity are satisfied with a large margin, there will always be at least one realization violating strict ergodicity. Thus, only conditional (approximate) ergodicity occurs in this case. Nevertheless, in calculation of the FRI zero drift in this situation, averaging over an ensemble of independent realizations of random inhomogeneities in the SMOF of an FRI loop can be performed with sufficient accuracy. As a result, calculations are simplified significantly. In the general case, when at least one of the conditions of ergodicity is not satisfied, averaging over temperature for each realization with subsequent averaging over the entire ensemble should be performed. It is shown also that, within this problem, we can speak only about quasi-ergodicity or emulation of ergodicity, since a change in the temperature of the SMOF of an FRI loop and successive enumeration of independent realizations of random inhomogeneities in the SMOF loop are radically different random processes. The parameters characterizing quasiperiodic temperature changes in the phase difference of counterpropagating waves at the FRI output are refined. 相似文献
977.
978.
V. B. Shikin 《JETP Letters》2002,75(1):29-33
The cyclotron resonance (CR) problem for electrons over a helium film occupying the lower part of a resonator is solved. This problem is shown to represent an example of the well-known problem on the behavior of a system of coupled oscillators. For such oscillators, the coupling constant is determined as a function of the problem parameters with its minimal value in zero magnetic field and its maximal value at resonance conditions, when the cyclotron frequency coincides with one of the resonator modes. The details of the CR absorption of microwave energy by the coupled system formed by 2D electrons and a resonator are calculated. The results are discussed in application to the known CR experiments with electrons over helium. 相似文献
979.
The contrast of interference pattern formed by two circularly polarized waves and by a linearly polarized wave and a circularly polarized one is discussed. The results are compared with that by two linear beams. It shows that the use of circular light in holographic fabrication of three-dimensional periodic microstructures may remove the necessity of beam ratio and polarization optimization needed in the interference of three linear noncoplanar beams and improve the uniform contrast of resultant pattern simultaneously. 相似文献
980.
A new theoretical model describing the emission and absorption dynamics in an ensemble of molecules under intense coherent pulsed pumping is developed on the basis of the concepts of cooperative light-induced luminescence (CLIL). The CLIL development is described within the framework of formalism of the system density matrix in the space of photon wave functions. It is shown that the fast growth of CLIL relates to the development of coherent states of the quantum field in the area of efficient cooperative interactions of molecules (coherence volume). A system of equations for the calculation of CLIL energy, population of excited states, and optical absorption of the system in dependence on the laser pump energy density is solved. The theoretical results obtained are in good agreement with the experimental data. 相似文献