全文获取类型
收费全文 | 2590篇 |
免费 | 445篇 |
国内免费 | 920篇 |
专业分类
测绘学 | 6篇 |
大气科学 | 21篇 |
地球物理 | 294篇 |
地质学 | 2910篇 |
海洋学 | 375篇 |
天文学 | 8篇 |
综合类 | 114篇 |
自然地理 | 227篇 |
出版年
2024年 | 8篇 |
2023年 | 27篇 |
2022年 | 76篇 |
2021年 | 76篇 |
2020年 | 96篇 |
2019年 | 82篇 |
2018年 | 97篇 |
2017年 | 89篇 |
2016年 | 110篇 |
2015年 | 97篇 |
2014年 | 129篇 |
2013年 | 175篇 |
2012年 | 184篇 |
2011年 | 137篇 |
2010年 | 130篇 |
2009年 | 170篇 |
2008年 | 169篇 |
2007年 | 195篇 |
2006年 | 172篇 |
2005年 | 182篇 |
2004年 | 182篇 |
2003年 | 168篇 |
2002年 | 141篇 |
2001年 | 122篇 |
2000年 | 144篇 |
1999年 | 130篇 |
1998年 | 101篇 |
1997年 | 98篇 |
1996年 | 96篇 |
1995年 | 105篇 |
1994年 | 52篇 |
1993年 | 46篇 |
1992年 | 41篇 |
1991年 | 23篇 |
1990年 | 22篇 |
1989年 | 22篇 |
1988年 | 13篇 |
1987年 | 11篇 |
1986年 | 9篇 |
1985年 | 9篇 |
1984年 | 4篇 |
1983年 | 8篇 |
1982年 | 4篇 |
1981年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有3955条查询结果,搜索用时 250 毫秒
61.
A New Model for Heat Flow in Extensional Basins: Estimating Radiogenic Heat Production 总被引:1,自引:0,他引:1
Radiogenic heat production (RHP) represents a significant fraction of surface heat flow, both on cratons and in sedimentary basins. RHP within continental crust—especially the upper crust—is high. RHP at any depth within the crust can be estimated as a function of crustal age. Mantle RHP, in contrast, is always low, contributing at most 1 to 2 mW/m2 to total heat flow. Radiogenic heat from any noncrystalline basement that may be present also contributes to total heat flow. RHP from metamorphic rocks is similar to or slightly lower than that from their precursor sedimentary rocks. When extension of the lithosphere occurs—as for example during rifting—the radiogenic contribution of each layer of the lithosphere and noncrystalline basement diminishes in direct proportion to the degree of extension of that layer. Lithospheric RHP today is somewhat less than in the distant past, as a result of radioactive decay. In modeling, RHP can be varied through time by considering the half lives of uranium, thorium, and potassium, and the proportional contribution of each of those elements to total RHP from basement. RHP from sedimentary rocks ranges from low for most evaporites to high for some shales, especially those rich in organic matter. The contribution to total heat flow of radiogenic heat from sediments depends strongly on total sediment thickness, and thus differs through time as subsidence and basin filling occur. RHP can be high for thick clastic sections. RHP in sediments can be calculated using ordinary or spectral gamma-ray logs, or it can be estimated from the lithology. 相似文献
62.
63.
64.
65.
66.
67.
The loess mounds are a newly discovered type of landforms on the Laizhou Bay plain south of the Bohai Sea. Research shows that they were formed in the late period of the late Pleistocene when the Bohai Sea was exposed in the period of late Wümu glacial age and changed into plain. As the exposed area is not protected by vegetation, the sediments at the sea bottom are blown and transported southward by strong north winds, and deposit on the coastal plains. As thick loess is accumulated, the loess mound landforms are formed in the direction of down wind. 相似文献
68.
69.
70.