全文获取类型
收费全文 | 3674篇 |
免费 | 593篇 |
国内免费 | 831篇 |
专业分类
测绘学 | 398篇 |
大气科学 | 350篇 |
地球物理 | 998篇 |
地质学 | 1533篇 |
海洋学 | 367篇 |
天文学 | 1015篇 |
综合类 | 178篇 |
自然地理 | 259篇 |
出版年
2024年 | 15篇 |
2023年 | 41篇 |
2022年 | 100篇 |
2021年 | 111篇 |
2020年 | 145篇 |
2019年 | 181篇 |
2018年 | 122篇 |
2017年 | 137篇 |
2016年 | 183篇 |
2015年 | 192篇 |
2014年 | 209篇 |
2013年 | 212篇 |
2012年 | 200篇 |
2011年 | 214篇 |
2010年 | 190篇 |
2009年 | 275篇 |
2008年 | 250篇 |
2007年 | 323篇 |
2006年 | 280篇 |
2005年 | 234篇 |
2004年 | 220篇 |
2003年 | 205篇 |
2002年 | 164篇 |
2001年 | 161篇 |
2000年 | 123篇 |
1999年 | 116篇 |
1998年 | 109篇 |
1997年 | 52篇 |
1996年 | 61篇 |
1995年 | 43篇 |
1994年 | 46篇 |
1993年 | 45篇 |
1992年 | 26篇 |
1991年 | 33篇 |
1990年 | 25篇 |
1989年 | 12篇 |
1988年 | 12篇 |
1987年 | 8篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 1篇 |
1977年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有5098条查询结果,搜索用时 15 毫秒
21.
22.
23.
Dark energy has a dramatic effect on the dynamics of the Universe, causing the recently discovered acceleration of the expansion. The dynamics are also central to the behaviour of the growth of large-scale structure, offering the possibility that observations of structure formation provide a sensitive probe of the cosmology and dark energy characteristics. In particular, dark energy with a time-varying equation of state can have an influence on structure formation stretching back well into the matter-dominated epoch. We analyse this impact, first calculating the linear perturbation results, including those for weak gravitational lensing. These dynamical models possess definite observable differences from constant equation of state models. Then we present a large-scale numerical simulation of structure formation, including the largest volume to date involving a time-varying equation of state. We find the halo mass function is well described by the Jenkins et al. mass function formula. We also show how to interpret modifications of the Friedmann equation in terms of a time-variable equation of state. The results presented here provide steps toward realistic computation of the effect of dark energy in cosmological probes involving large-scale structure, such as cluster counts, the Sunyaev–Zel'dovich effect or weak gravitational lensing. 相似文献
24.
25.
Gopal C. Kilambi Praveen Nagar N. Kameswara Rao 《Journal of Astrophysics and Astronomy》1992,13(2):175-194
Mid-ultraviolet and optical photometric analysis of helium stars are presented. A linear relation exists between the effective
temperature derived from model atmospheres and (1965-V)0 index. The effective temperatures derived from (1965-V)0 index are somewhat higher than that of MK spectral type estimates especially for late B-type helium objects. 相似文献
26.
Kleomenis Tsiganis Harry Varvoglis Rudolf Dvorak 《Celestial Mechanics and Dynamical Astronomy》2005,92(1-3):71-87
It has recently been shown that Jupiter Trojans may exhibit chaotic behavior, a fact that has put in question their presumed long term stability. Previous numerical results suggest a slow dispersion of the Trojan swarms, but the extent of the ‘effective’ stability region in orbital elements space is still an open problem. In this paper, we tackle this problem by means of extensive numerical integrations. First, a set of 3,200 fictitious objects and 667 numbered Trojans is integrated for 4 Myrs and their Lyapunov time, TL, is estimated. The ones following chaotic orbits are then integrated for 1 Gyr, or until they escape from the Trojan region. The results of these experiments are presented in the form of maps of TLand the escape time, TE, in the space of proper elements. An effective stability region for 1 Gyr is defined on these maps, in which chaotic orbits also exist. The distribution of the numbered Trojans follows closely the TE=1 Gyr level curve, with 86% of the bodies lying inside and 14% outside the stability region. This result is confirmed by a 4.5 Gyr integration of the 246 chaotic numbered Trojans, which showed that 17% of the numbered Trojans are unstable over the age of the solar system. We show that the size distributions of the stable and unstable populations are nearly identical. Thus, the existence of unstable bodies should not be the result of a size-dependent transport mechanism but, rather, the result of chaotic diffusion. Finally, in the large chaotic region that surrounds the stability zone, a statistical correlation between TLandTE is found. 相似文献
27.
28.
29.
S.W. Allen 《Astrophysics and Space Science》2003,285(1):247-256
Chandra X-ray observations of rich, dynamically relaxed galaxy clusters allow the properties of the X-ray gas and the total
gravitating mass to be determined precisely. Here, we discuss how Chandra observations may be used as a powerful tool for
cosmological studies. By combining Chandra X-ray results on the X-ray gas mass fractions in clusters with independent measurements
of the Hubble constant and the mean baryonic matter density of the universe, we obtain a tight constraint on the mean total
matter density of the universe, Οm, and an interesting constraint on the cosmological constant, ΟΛ. Using these results, together with the observed local X-ray luminosity function of the most X-ray luminous galaxy clusters,
a mass-luminosity relation determined from Chandra and ROSAT X-ray data and weak gravitational lensing observations, and the
mass function predicted by numerical simulations, we obtain a precise constraint on the normalization of the power spectrum
of density fluctuations in the nearby universe,σ8. We compare our results with those obtained from other, independent methods.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
30.