全文获取类型
收费全文 | 2939篇 |
免费 | 737篇 |
国内免费 | 588篇 |
专业分类
测绘学 | 235篇 |
大气科学 | 309篇 |
地球物理 | 795篇 |
地质学 | 1530篇 |
海洋学 | 568篇 |
天文学 | 61篇 |
综合类 | 317篇 |
自然地理 | 449篇 |
出版年
2024年 | 12篇 |
2023年 | 35篇 |
2022年 | 102篇 |
2021年 | 138篇 |
2020年 | 164篇 |
2019年 | 132篇 |
2018年 | 130篇 |
2017年 | 129篇 |
2016年 | 174篇 |
2015年 | 161篇 |
2014年 | 208篇 |
2013年 | 246篇 |
2012年 | 211篇 |
2011年 | 232篇 |
2010年 | 190篇 |
2009年 | 187篇 |
2008年 | 193篇 |
2007年 | 195篇 |
2006年 | 181篇 |
2005年 | 144篇 |
2004年 | 135篇 |
2003年 | 93篇 |
2002年 | 106篇 |
2001年 | 104篇 |
2000年 | 93篇 |
1999年 | 75篇 |
1998年 | 83篇 |
1997年 | 68篇 |
1996年 | 60篇 |
1995年 | 35篇 |
1994年 | 48篇 |
1993年 | 35篇 |
1992年 | 30篇 |
1991年 | 29篇 |
1990年 | 12篇 |
1989年 | 20篇 |
1988年 | 21篇 |
1987年 | 7篇 |
1986年 | 4篇 |
1985年 | 11篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 8篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1954年 | 4篇 |
排序方式: 共有4264条查询结果,搜索用时 62 毫秒
131.
A combined gravity map over the Indian Peninsular Shield (IPS) and adjoining oceans brings out well the inter-relationships between the older tectonic features of the continent and the adjoining younger oceanic features. The NW–SE, NE–SW and N–S Precambrian trends of the IPS are reflected in the structural trends of the Arabian Sea and the Bay of Bengal suggesting their probable reactivation. The Simple Bouguer anomaly map shows consistent increase in gravity value from the continent to the deep ocean basins, which is attributed to isostatic compensation due to variations in the crustal thickness. A crustal density model computed along a profile across this region suggests a thick crust of 35–40 km under the continent, which reduces to 22/20–24 km under the Bay of Bengal with thick sediments of 8–10 km underlain by crustal layers of density 2720 and 2900/2840 kg/m3. Large crustal thickness and trends of the gravity anomalies may suggest a transitional crust in the Bay of Bengal up to 150–200 km from the east coast. The crustal thickness under the Laxmi ridge and east of it in the Arabian Sea is 20 and 14 km, respectively, with 5–6 km thick Tertiary and Mesozoic sediments separated by a thin layer of Deccan Trap. Crustal layers of densities 2750 and 2950 kg/m3 underlie sediments. The crustal density model in this part of the Arabian Sea (east of Laxmi ridge) and the structural trends similar to the Indian Peninsular Shield suggest a continent–ocean transitional crust (COTC). The COTC may represent down dropped and submerged parts of the Indian crust evolved at the time of break-up along the west coast of India and passage of Reunion hotspot over India during late Cretaceous. The crustal model under this part also shows an underplated lower crust and a low density upper mantle, extending over the continent across the west coast of India, which appears to be related to the Deccan volcanism. The crustal thickness under the western Arabian Sea (west of the Laxmi ridge) reduces to 8–9 km with crustal layers of densities 2650 and 2870 kg/m3 representing an oceanic crust. 相似文献
132.
133.
用遗传算法反演地壳的变密度模型 总被引:7,自引:1,他引:7
用青藏高原布格重力异常资料 ,结合亚东 格尔木地学断面得到的Moho面结构 ,反演了青藏高原中部地壳内密度随深度变化的指数分布函数 ,试验得出地壳表层与地幔的密度差约为 - 0 .92 6 g·cm-3 ,地壳的平均密度值为 2 .75 0 g·cm-3 。 相似文献
134.
针对传统的边缘提取方法大部分不适应高光谱数据的特点,提出了基于光谱空间密度分析边缘提取的思想。在分组主分量变换提取第一主分量作为特征维的基础上,采用面向对象的二次判别边缘的方法,通过立体判决将光谱空间中低密度超椭球体集群视为真实边缘点集群。试验表明,此方法是合理可行的。 相似文献
135.
136.
Introduction Sichuan-Yunnan region, located in the east margin of Qinghai-Xizang (Tibetean) Plateau, is a transitional zone between the rapidly upheaving Tibetean Plateau and relatively steady Yangtze Platform. Under the pressure exerted by the northward movement of Indian Plate, Sichuan-Yunnan region has been undergone strong deformation and regmagenesis, becoming one of the regions with the most intensive seismicity in the world. The research on the tectonics and seismicity there is alw… 相似文献
137.
Roberto Sulpizio Daniela Mele Pierfrancesco Dellino Luigi La Volpe 《Bulletin of Volcanology》2005,67(8):743-767
The combined use of field investigation and laboratory analyses allowed the detailed stratigraphic reconstruction of the Pollena eruption (472 AD) of Somma-Vesuvius. Three main eruptive phases were recognized, related either to changes in the eruptive processes and/or to relative changes of melt composition. The eruption shows a pulsating behavior with deposition of pyroclastic fall beds and generation of dilute and dense pyroclastic density currents (PDC). The eruptive mechanisms and transportation dynamics were reconstructed for the whole eruption. Column heights were between 12 and 20 km, corresponding to mass discharge rates (MDR) of 7×106 kg/s and 3.4×107 kg/s. Eruptive dynamics were driven by magmatic fragmentation of a phono-tephritic to tephri-phonolitic magma during Phases I and II, whereas phreatomagmatic fragmentation dominated Phase III. Magma composition varies between phonolitic and tephritic-phonolitic, with melt viscosity likely not in excess of 103 Pa s. The volume of the pyroclastic fall deposits, calculated by using of proximal isopachs, is 0.44 km3. This increases to 1.38 km3 if ash volumes are extrapolated on a log thickness vs. square root area diagram using one distal isopach and column height.Editorial responsibility: R Cioni 相似文献
138.
139.
Craig T. Simmons 《Hydrogeology Journal》2005,13(1):116-119
140.