全文获取类型
收费全文 | 31340篇 |
免费 | 4695篇 |
国内免费 | 6732篇 |
专业分类
测绘学 | 3346篇 |
大气科学 | 4076篇 |
地球物理 | 7609篇 |
地质学 | 14775篇 |
海洋学 | 4188篇 |
天文学 | 2518篇 |
综合类 | 1992篇 |
自然地理 | 4263篇 |
出版年
2024年 | 108篇 |
2023年 | 350篇 |
2022年 | 842篇 |
2021年 | 1071篇 |
2020年 | 1229篇 |
2019年 | 1580篇 |
2018年 | 1094篇 |
2017年 | 1422篇 |
2016年 | 1390篇 |
2015年 | 1515篇 |
2014年 | 1891篇 |
2013年 | 2132篇 |
2012年 | 1886篇 |
2011年 | 2047篇 |
2010年 | 1600篇 |
2009年 | 2174篇 |
2008年 | 2179篇 |
2007年 | 2269篇 |
2006年 | 2253篇 |
2005年 | 1751篇 |
2004年 | 1688篇 |
2003年 | 1417篇 |
2002年 | 1140篇 |
2001年 | 1048篇 |
2000年 | 930篇 |
1999年 | 878篇 |
1998年 | 871篇 |
1997年 | 675篇 |
1996年 | 562篇 |
1995年 | 498篇 |
1994年 | 438篇 |
1993年 | 378篇 |
1992年 | 280篇 |
1991年 | 213篇 |
1990年 | 174篇 |
1989年 | 168篇 |
1988年 | 131篇 |
1987年 | 84篇 |
1986年 | 65篇 |
1985年 | 72篇 |
1984年 | 48篇 |
1983年 | 18篇 |
1982年 | 29篇 |
1981年 | 24篇 |
1980年 | 22篇 |
1978年 | 15篇 |
1977年 | 20篇 |
1976年 | 25篇 |
1973年 | 17篇 |
1971年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
81.
Annamaria Borriello Paolo Salucci 《Monthly notices of the Royal Astronomical Society》2001,323(2):285-292
We use high-quality optical rotation curves of nine low-luminosity disc galaxies to obtain the velocity profiles of the surrounding dark matter haloes. We find that they increase linearly with radius at least out to the edge of the stellar disc, implying that, over the entire stellar region, the density of the dark halo is about constant.
The properties of the mass structure of these haloes are similar to those found for a number of dwarf and low surface brightness galaxies, but provide a more substantial evidence of the discrepancy between the halo mass distribution predicted in the cold dark matter scenario and those actually detected around galaxies. We find that the density law proposed by Burkert reproduces the halo rotation curves, with halo central densities ( ρ0 ∼1–4×10−24 g cm−3 ) and core radii ( r 0 ∼5–15 kpc) scaling as ρ 0 ∝ r 0 −2/3 . 相似文献
The properties of the mass structure of these haloes are similar to those found for a number of dwarf and low surface brightness galaxies, but provide a more substantial evidence of the discrepancy between the halo mass distribution predicted in the cold dark matter scenario and those actually detected around galaxies. We find that the density law proposed by Burkert reproduces the halo rotation curves, with halo central densities ( ρ
82.
83.
84.
Robert R. Twilley 《Estuarine, Coastal and Shelf Science》1985,20(5):543-557
The magnitude and seasonality of organic carbon exchange was estimated for two basin mangrove forests in Rookery Bay, Florida. Runoff and tidal inundation in the forests were seasonal with half the annual total of each occurring from August to October. In each forest there were 152 tides yr?1 with a cumulative depth of about 12 m. Total organic carbon increased in bay waters exporting from the mangroves following a flood tide and peak concentrations were associated with export due to rainfall. The amount of net export from each basin forest was similar, although the concentration of organic carbon in each were different. Monthly net organic carbon export was proportional to the cumulative tidal amplitude within the forest. Total organic carbon export was 64 gC m?2 yr?1 and DOC was 75% of the total. A comparison of organic carbon export among riverine, fringe and basin mangroves suggests that tidal hydrology influences the proportion of litter fall that is exported from mangroves; and the magnitude of this organic carbon export from mangroves is related to the cumulative tidal amplitude within the forests. 相似文献
85.
86.
Jacques Laskar 《Celestial Mechanics and Dynamical Astronomy》1993,56(1-2):191-196
Frequency analysis is a new method for analyzing the stability of orbits in a conservative dynamical system. It was first devised in order to study the stability of the solar system (Laskar, Icarus, 88, 1990). It is a powerful method for analyzing weakly chaotic motion in hamiltonian systems or symplectic maps. For regular motions, it yields an analytical representation of the solutions. In cases of 2 degrees of freedom system with monotonous torsion, precise numerical criterions for the destruction of KAM tori can be found. For a 4D symplectic map, plotting the frequency map in the frequency plane provides a clear representation of the global dynamics and describes the actual Arnold web of the system. 相似文献
87.
88.
89.
90.
案例推理的地学应用背景和方法 总被引:3,自引:1,他引:2
案例推理 (CBR)研究 ,是人类认知的一种合理性模型 ,接近于人类认识、解决问题最原始的思维方式 ,具有在无法获取机理模型、确定规则或统计模型时 ,采用简单的历史相似性推理实现问题的定量求解和预测 ,成为人工智能领域近年来的研究热点。 相似文献