全文获取类型
收费全文 | 3563篇 |
免费 | 489篇 |
国内免费 | 455篇 |
专业分类
测绘学 | 340篇 |
大气科学 | 407篇 |
地球物理 | 1183篇 |
地质学 | 896篇 |
海洋学 | 308篇 |
天文学 | 583篇 |
综合类 | 191篇 |
自然地理 | 599篇 |
出版年
2024年 | 7篇 |
2023年 | 22篇 |
2022年 | 67篇 |
2021年 | 95篇 |
2020年 | 107篇 |
2019年 | 118篇 |
2018年 | 88篇 |
2017年 | 94篇 |
2016年 | 114篇 |
2015年 | 121篇 |
2014年 | 161篇 |
2013年 | 205篇 |
2012年 | 134篇 |
2011年 | 215篇 |
2010年 | 171篇 |
2009年 | 251篇 |
2008年 | 218篇 |
2007年 | 258篇 |
2006年 | 237篇 |
2005年 | 212篇 |
2004年 | 189篇 |
2003年 | 166篇 |
2002年 | 144篇 |
2001年 | 115篇 |
2000年 | 137篇 |
1999年 | 108篇 |
1998年 | 101篇 |
1997年 | 114篇 |
1996年 | 98篇 |
1995年 | 72篇 |
1994年 | 83篇 |
1993年 | 51篇 |
1992年 | 55篇 |
1991年 | 34篇 |
1990年 | 25篇 |
1989年 | 28篇 |
1988年 | 19篇 |
1987年 | 21篇 |
1986年 | 12篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 2篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 1篇 |
1971年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有4507条查询结果,搜索用时 156 毫秒
1.
2.
Sergei A. Klioner 《Celestial Mechanics and Dynamical Astronomy》1996,66(4):345-363
Intermediate orbit for general planetary theory is constructed in the form of multivariate Fourier series with numerical coefficients. The structure and efficiency of the derived series are illustrated by giving various statistical properties of the coefficients.The ability of the recently proposed elliptic function approach to compress the Fourier series representing the intermediate orbit is investigated. Our results confirm that when mutual perturbations of a pair of planets are considered the elliptic function approach is quite efficient and allows one to compress the series substantially. However, when perturbations of three or more planets are under study the elliptic function approach does not give any advantages. 相似文献
3.
4.
5.
We have derived the galaxy luminosity function in various regions of the cluster of galaxies Abell 496 from a wide field image
in the I band. A Schechter function fit in the 17≤ IAB ≤22(–19.5≤ MIAB ≤ –14.5) magnitude interval gives a steep power law index, which is somewhat steeper in the outer regions than in the inner
zones. This result agrees with previous findings obtained by several teams on the Coma cluster and can be interpreted as due
to the fact that faint galaxies are accreted by large ones in the central regions.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
Yunfei Bao Shengbo Chen 《东北亚地学研究》2006,9(1):100-108
IntroductionThe radiance leaving the earth-atmosphere sys-tem which can be sensed by a satellite borne ra-diometer is the sum of radiation emission fromtheearth surface and each atmospheric level that aretransmittedtothe top of the atmosphere.The radia-tion emissionfromthe earthsurface andthe radianceof each atmospheric level can be separated fromtheradiance at the top the atmospheric level a satellitemeasured.Thus,the earth surface parameters willbe retrieved from the surface radiance after a… 相似文献
7.
We present a new general scheme for calculating the structure and dynamics of radiation-pressure-driven photoionized flows. The new method goes one step beyond the Sobolev approximation. It involves a numerical solution of the radiative transfer in absorption lines, including the effects of differential expansion and line interactions such as line locking and blanketing. We also present a new scheme for calculating the radiation pressure due to trapped line photons in finite, differentially expanding flows. We compare our results for the radiation pressure force with those obtained using the Sobolev approximation and show the limitations of the latter. In particular, we demonstrate that the Sobolev method gives a poor approximation near discontinuity surfaces and its neglect of line blanketing can lead to erroneous results in high-velocity flows. We combine the newly calculated radiation pressure force with self-consistent photoionization and thermal calculations to study the dynamics and spectral features of broad absorption-line flows and highly ionized gas flows in active galactic nuclei (AGN). A comparison with Sobolev-type calculations shows that the latter overestimates the terminal velocity of the flow and, conversely, underestimates its opacity. We also show that line locking on broad emission lines can have a significant effect on the dynamics and spectral features of AGN flows. 相似文献
8.
A. G. Nikoghossian 《Astrophysics》2006,49(2):228-239
The problem of finding statistical averages which characterize the radiation field in a semi-infinite atmosphere has been
discussed by the author in a series of papers. In this paper some of the results obtained there are generalized to media of
finite optical thickness. The average number of scattering events undergone by a photon during its random walk in an atmosphere
and the average time required for this are determined. Three different types of averages are considered, depending on the
photon characteristics over which the averages are taken. Special attention is devoted to the asymptotic behavior of these
quantities for media with large optical depths taking the influence of continuum absorption into account.
__________
Translated from Astrofizika, Vol. 49, No. 2, pp. 263–275 (May 2006). 相似文献
9.
The effect of ocean wave breaking as a non-Bragg mechanism on backscattering cross-section and modulation transfer functions (MTF) of radar was investigated based on Bragg resonance theory and parametric method. The result showed that the additional effect of wave breaking on backscattering cross-section is not more than 20% except for the small incident angle of VV polarized electromagnetic (e.m.) wave but is significant for HH polarized e.m. wave. Breaking waves lead to increase in the modulus of tilt modulation MTF and the larger the wind speed, the faster the increase. For large incident angle, the modulus of tilt modulation MTF with wave breaking decreases quickly with incident angle for HH polarization and approach to that without wave breaking for VV polarization. The hydrodynamic MTF increases 30%-60% when considering wave breaking and the increase is larger for HH polarization than for VV polarization. 相似文献
10.
A. G. Nikoghossian 《Astrophysics》2004,47(3):412-421
The approach proposed in the previous parts of this series of papers is used to solve the radiative transfer problem in scattering and absorbing multicomponent atmospheres. Linear recurrence relations are obtained for both the reflectance and transmittance of these kinds of atmospheres, as well as for the emerging intensities when the atmosphere contains energy sources. Spectral line formation in a one-dimensional inhomogeneous atmosphere is examined as an illustration of the possibility of generalizing our approach to the matrix case. It is shown that, in this case as well, the question reduces to solving an initial value problem for linear differential equations. Some numerical calculations are presented. 相似文献