全文获取类型
收费全文 | 900篇 |
免费 | 41篇 |
国内免费 | 7篇 |
专业分类
测绘学 | 24篇 |
大气科学 | 74篇 |
地球物理 | 174篇 |
地质学 | 281篇 |
海洋学 | 63篇 |
天文学 | 231篇 |
综合类 | 2篇 |
自然地理 | 99篇 |
出版年
2021年 | 13篇 |
2020年 | 19篇 |
2019年 | 20篇 |
2018年 | 22篇 |
2017年 | 15篇 |
2016年 | 32篇 |
2015年 | 24篇 |
2014年 | 20篇 |
2013年 | 41篇 |
2012年 | 25篇 |
2011年 | 24篇 |
2010年 | 35篇 |
2009年 | 54篇 |
2008年 | 40篇 |
2007年 | 33篇 |
2006年 | 40篇 |
2005年 | 32篇 |
2004年 | 39篇 |
2003年 | 35篇 |
2002年 | 35篇 |
2001年 | 16篇 |
2000年 | 28篇 |
1999年 | 17篇 |
1998年 | 18篇 |
1997年 | 14篇 |
1996年 | 10篇 |
1995年 | 13篇 |
1994年 | 9篇 |
1993年 | 14篇 |
1992年 | 4篇 |
1991年 | 6篇 |
1990年 | 7篇 |
1988年 | 8篇 |
1987年 | 15篇 |
1986年 | 4篇 |
1985年 | 14篇 |
1984年 | 19篇 |
1983年 | 13篇 |
1982年 | 8篇 |
1981年 | 15篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1978年 | 5篇 |
1977年 | 7篇 |
1976年 | 9篇 |
1975年 | 10篇 |
1974年 | 4篇 |
1973年 | 4篇 |
1972年 | 5篇 |
1970年 | 4篇 |
排序方式: 共有948条查询结果,搜索用时 281 毫秒
101.
The microlensing optical depth to Baade's Window constrains the minimum total mass in baryonic matter within the Solar circle to be greater than ∼ , assuming the inner Galaxy is barred with viewing angle ∼20°. From the kinematics of solar neighbourhood stars, the local surface density of dark matter is ∼ . We construct cuspy haloes normalized to the local dark matter density and calculate the circular-speed curve of the halo in the inner Galaxy. This is added in quadrature to the rotation curve provided by the stellar and ISM discs, together with a bar sufficiently massive so that the baryonic matter in the inner Galaxy reproduces the microlensing optical depth. Such models violate the observational constraint provided by the tangent-velocity data in the inner Galaxy (typically at radii . The high baryonic contribution required by the microlensing is consistent with implications from hydrodynamical modelling and the pattern speed of the Galactic bar. We conclude that the cuspy haloes favoured by the cold dark matter cosmology (and its variants) are inconsistent with the observational data on the Galaxy. 相似文献
102.
J.Kleyna M. I.Wilkinson N. W.Evans G.Gilmore C.Frayn 《Monthly notices of the Royal Astronomical Society》2002,330(4):792-806
We present stellar radial velocity data for the Draco dwarf spheroidal (dSph) galaxy obtained using the AF2/WYFFOS instrument combination on the William Herschel Telescope. Our data set consists of 186 member stars, 159 of which have good quality velocities, extending to a magnitude V ≈19.5 with a mean velocity precision of ≈2 km s−1 . As this survey is based on a high-precision photometric target list, it contains many more Draco members at large radii. For the first time, this allows a robust determination of the radial behaviour of the velocity dispersion in a dSph.
We find statistically strong evidence of a rising velocity dispersion consistent with a dark matter halo that has a gently rising rotation curve. There is a <2 σ signature of rotation about the long axis, inconsistent with tidal disruption as the source of the rising dispersion. By comparing our data set with earlier velocities, we find that Draco probably has a binary distribution and fraction comparable to those in the solar neighbourhood.
We apply a novel maximum likelihood algorithm and fit the velocity data to a two parameter spherical model with an adjustable dark matter content and velocity anisotropy. Draco is best fit by a weakly tangentially anisotropic distribution of stellar orbits in a dark matter halo with a very slowly rising rotation law ( vcirc ∝ r 0.17 ) . We are able to rule out both a mass-follows-light distribution and an extended halo with a harmonic core at the 2.5 to 3 σ significance level, depending on the details of our assumptions about Draco's stellar binary population. Our modelling lends support to the idea that the dark matter in dwarf spheroidals is distributed in the form of massive, nearly isothermal haloes. 相似文献
We find statistically strong evidence of a rising velocity dispersion consistent with a dark matter halo that has a gently rising rotation curve. There is a <2 σ signature of rotation about the long axis, inconsistent with tidal disruption as the source of the rising dispersion. By comparing our data set with earlier velocities, we find that Draco probably has a binary distribution and fraction comparable to those in the solar neighbourhood.
We apply a novel maximum likelihood algorithm and fit the velocity data to a two parameter spherical model with an adjustable dark matter content and velocity anisotropy. Draco is best fit by a weakly tangentially anisotropic distribution of stellar orbits in a dark matter halo with a very slowly rising rotation law ( v
103.
104.
105.
106.
Climate Dynamics - Regional climate models (RCM) are an important tool for simulating atmospheric information at finer resolutions often of greater relevance to local scale climate change impact... 相似文献
107.
Abstract On the basis of two well‐known ozone‐weather relationships, an algorithm is proposed that estimates total ozone amounts using readily available meteorological information. The technique has been labelled METOZ from Meteorological Total Ozone. A rationale and derivation of the technique is presented. METOZ total ozone amounts were generated for Toronto and Edmonton locations and compared with ground‐based Brewer spectrophotometer measures for these two stations in the Canadian ozone monitoring network for data from January to April 1989. Per cent differences between METOZ and Brewer total ozone measurements were calculated and are presented. This mid‐latitude wînter metoz algorithm was also used to produce a hemispherical total ozone field for 16 March 1986, which was compared with the corresponding TOMS data to demonstrate other potential applications of the technique. 相似文献
108.
Variations in the abundance and distribution of pelagic tuna populations have been associated with large-scale climate indices such as the Southern Oscillation Index in the Pacific Ocean and the North Atlantic Oscillation in the Atlantic Ocean. Similarly to the Pacific and Atlantic, variability in the distribution and catch rates of tuna species have also been observed in association with the Indian Ocean Dipole (IOD), a basin-scale pattern of sea surface and subsurface temperatures that affect climate in the Indian Ocean. The environmental processes associated with the IOD that drive variability in tuna populations, however, are largely unexplored. To better understand these processes, we investigated longline catch rates of yellowfin tuna and their distributions in the western Indian Ocean in relation to IOD events, sea surface water temperatures (SST) and estimates of net primary productivity (NPP). Catch per unit effort (CPUE) was observed to be negatively correlated to the IOD with a periodicity centred around 4 years. During positive IOD events, SSTs were relatively higher, NPP was lower, CPUE decreased and catch distributions were restricted to the northern and western margins of the western Indian Ocean. During negative IOD events, lower SSTs and higher NPP were associated with increasing CPUE, particularly in the Arabian Sea and seas surrounding Madagascar, and catches expanded into central regions of the western Indian Ocean. These findings provide preliminary insights into some of the key environmental features driving the distribution of yellowfin tuna in the western Indian Ocean and associated variability in fisheries catches. 相似文献
109.
The intermediate polar (IP) HT Cam is unusual in that it shows no evidence for dense absorption in its spectrum. We analyse an XMM–Newton observation of this star, which confirms the absence of absorption and shows that the X-ray spin pulse is energy independent. The modulation arises solely from occultation effects and can be reproduced by a simple geometrical model in which the lower accretion footprint is fainter than the upper one.
We suggest that the lack of opacity in the accretion columns of HT Cam, and also of EX Hya and V1025 Cen, results from a low accretion rate owing to their being below the cataclysmic variable period gap. 相似文献
We suggest that the lack of opacity in the accretion columns of HT Cam, and also of EX Hya and V1025 Cen, results from a low accretion rate owing to their being below the cataclysmic variable period gap. 相似文献
110.