全文获取类型
收费全文 | 625362篇 |
免费 | 5675篇 |
国内免费 | 1796篇 |
专业分类
化学 | 311859篇 |
晶体学 | 8882篇 |
力学 | 32350篇 |
综合类 | 20篇 |
数学 | 96633篇 |
物理学 | 183089篇 |
出版年
2021年 | 4871篇 |
2020年 | 5314篇 |
2019年 | 5937篇 |
2018年 | 17585篇 |
2017年 | 17410篇 |
2016年 | 17005篇 |
2015年 | 7448篇 |
2014年 | 11062篇 |
2013年 | 25000篇 |
2012年 | 22516篇 |
2011年 | 32877篇 |
2010年 | 22177篇 |
2009年 | 22591篇 |
2008年 | 27699篇 |
2007年 | 29405篇 |
2006年 | 20052篇 |
2005年 | 18884篇 |
2004年 | 17919篇 |
2003年 | 16505篇 |
2002年 | 15595篇 |
2001年 | 16809篇 |
2000年 | 12751篇 |
1999年 | 9918篇 |
1998年 | 8438篇 |
1997年 | 8056篇 |
1996年 | 7792篇 |
1995年 | 7001篇 |
1994年 | 6872篇 |
1993年 | 6718篇 |
1992年 | 7249篇 |
1991年 | 7597篇 |
1990年 | 7240篇 |
1989年 | 7129篇 |
1988年 | 7026篇 |
1987年 | 6920篇 |
1986年 | 6571篇 |
1985年 | 8454篇 |
1984年 | 8538篇 |
1983年 | 6899篇 |
1982年 | 7060篇 |
1981年 | 6948篇 |
1980年 | 6439篇 |
1979年 | 7031篇 |
1978年 | 7260篇 |
1977年 | 7237篇 |
1976年 | 7248篇 |
1975年 | 6678篇 |
1974年 | 6642篇 |
1973年 | 6782篇 |
1972年 | 4958篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
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
42.
43.
44.
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
45.
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
46.
M. Heusler 《General Relativity and Gravitation》1991,23(2):189-207
The field equations for homogeneous models in an arbitrary number of dimensions form a Hamiltonian system with constraint forces. Due to the monotonic behavior of the determinant of the induced metric, the evolution of the system can be interpreted as the motion of a particle in an explicitly time-dependent potential. Considering vacuum models, we show that this explicit time-dependence can be eliminated. Using the scaling properties of the Ricci tensor we obtain an autonomous system, for which we can also find a Liapunov function in terms of the n-dimensional Ricci curvature. 相似文献
47.
48.
49.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 51, No. 2, pp. 212–217, August, 1989. 相似文献
50.