全文获取类型
收费全文 | 356312篇 |
免费 | 2422篇 |
国内免费 | 824篇 |
专业分类
化学 | 178717篇 |
晶体学 | 5469篇 |
力学 | 17841篇 |
综合类 | 11篇 |
数学 | 41976篇 |
物理学 | 115544篇 |
出版年
2020年 | 3249篇 |
2019年 | 3806篇 |
2018年 | 5375篇 |
2017年 | 5428篇 |
2016年 | 7134篇 |
2015年 | 3825篇 |
2014年 | 6561篇 |
2013年 | 15028篇 |
2012年 | 11785篇 |
2011年 | 14107篇 |
2010年 | 10609篇 |
2009年 | 10598篇 |
2008年 | 13131篇 |
2007年 | 13265篇 |
2006年 | 12308篇 |
2005年 | 11012篇 |
2004年 | 10373篇 |
2003年 | 9306篇 |
2002年 | 9297篇 |
2001年 | 10603篇 |
2000年 | 8028篇 |
1999年 | 6155篇 |
1998年 | 5260篇 |
1997年 | 5106篇 |
1996年 | 4701篇 |
1995年 | 4382篇 |
1994年 | 4230篇 |
1993年 | 4129篇 |
1992年 | 4503篇 |
1991年 | 4755篇 |
1990年 | 4608篇 |
1989年 | 4496篇 |
1988年 | 4470篇 |
1987年 | 4451篇 |
1986年 | 4141篇 |
1985年 | 5286篇 |
1984年 | 5557篇 |
1983年 | 4670篇 |
1982年 | 4920篇 |
1981年 | 4804篇 |
1980年 | 4471篇 |
1979年 | 4819篇 |
1978年 | 5060篇 |
1977年 | 5152篇 |
1976年 | 5290篇 |
1975年 | 4883篇 |
1974年 | 4834篇 |
1973年 | 5096篇 |
1972年 | 3667篇 |
1971年 | 3133篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
A new geometrical method to determine the surface damage threshold for ultrashort pulses is presented. It consists in the formation of a surface damage profile by a movement of the sample across the laser beam focus. A single measurement of the maximum transversal dimension of this damage profile, which depends solely on the laser beam power, is used to calculate the local damage threshold intensity. It is also theoretically shown that the damage in the transverse dimension can be controlled under the diffraction-limited spot. 相似文献
22.
V. I. Dashkevich 《Journal of Applied Spectroscopy》2002,69(6):862-870
Based on a semiclassical theory, investigations were made of the dynamics and spectral composition of pulsed generation with self-injection of priming radiation from the active part of a three-mirror linear resonator, the passive part of which contains an active loss modulator and serves as the output reflector of the laser. It is shown that there exists a range of resonator parameters at which pulsed lasing has virtually a single frequency irrespective of the detuning of the frequencies of the priming radiation and of the nearest eigenmode of the composite resonator. Considering graphically the phase conditions of generation, it is established that among pulsed lasers with self-injection of priming radiation which are constructed on the basis of three-mirror linear and branched resonators, the most efficient for creating single-frequency generation are those in which the length of the main resonator, where generation of the pulse occurs, is larger than the length of the additional one intended for forming the priming radiation. With an inverse ratio of the lengths of the resonators, the conditions of single-frequency pulsed generation becomes dependent on the priming radiation frequency. 相似文献
23.
24.
A simple scheme is developed for treatment of vertical bed topography in shallow water flows. The effect of the vertical step on flows is modelled with the shallow water equations including local energy loss terms. The bed elevation is denoted with zb‐ for the left and zb+ for the right values at each grid point, hence exactly representing a discontinuity in the bed topography. The surface gradient method (SGM) is generalized to reconstruct water depths at cell interfaces involving a vertical step so that the fluxes at the cell interfaces can accurately be calculated with a Riemann solver. The scheme is verified by predicting a surge crossing a step, a tidal flow over a step and dam‐break flows on wet/dry beds. The results have shown good agreements compared with analytical solutions and available experimental data. The scheme is efficient, robust, and may be used for practical flow calculations. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
25.
A. R. Volkov B. V. Shul'gin T. I. Polupanova V. N. Lebedev A. A. Nagornyi V. L. Petrov Yu. F. Kargin 《Journal of Applied Spectroscopy》1991,54(6):585-590
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 54, No. 6, pp. 970–975, June, 1991. 相似文献
26.
27.
28.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 51, No. 2, pp. 212–217, August, 1989. 相似文献
29.
30.
We demonstrate a method that permits to obtain generalized solutions for some quasilinear equations and systems of hyperbolic
type. The corresponding variational principle is constructed using the theory of equilibrium of a potential in an external
field.
Dedicated to the memory of B. M. Levitan
Supported by RFBR grants Nos. 05-01-00522 and NSh-1551.2003.1, by Program No. 1 of the Branch of Mathematics, Russian Academy
of Sciences, and by INTAS project No. 03-51-6637. 相似文献