全文获取类型
收费全文 | 4399篇 |
免费 | 719篇 |
国内免费 | 667篇 |
专业分类
测绘学 | 44篇 |
大气科学 | 288篇 |
地球物理 | 1954篇 |
地质学 | 1426篇 |
海洋学 | 644篇 |
天文学 | 584篇 |
综合类 | 340篇 |
自然地理 | 505篇 |
出版年
2024年 | 12篇 |
2023年 | 41篇 |
2022年 | 116篇 |
2021年 | 142篇 |
2020年 | 141篇 |
2019年 | 142篇 |
2018年 | 141篇 |
2017年 | 151篇 |
2016年 | 137篇 |
2015年 | 144篇 |
2014年 | 209篇 |
2013年 | 220篇 |
2012年 | 195篇 |
2011年 | 179篇 |
2010年 | 199篇 |
2009年 | 345篇 |
2008年 | 331篇 |
2007年 | 315篇 |
2006年 | 276篇 |
2005年 | 251篇 |
2004年 | 238篇 |
2003年 | 226篇 |
2002年 | 164篇 |
2001年 | 151篇 |
2000年 | 228篇 |
1999年 | 189篇 |
1998年 | 173篇 |
1997年 | 135篇 |
1996年 | 124篇 |
1995年 | 98篇 |
1994年 | 79篇 |
1993年 | 63篇 |
1992年 | 65篇 |
1991年 | 44篇 |
1990年 | 20篇 |
1989年 | 26篇 |
1988年 | 13篇 |
1987年 | 14篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1979年 | 7篇 |
1978年 | 2篇 |
1954年 | 3篇 |
排序方式: 共有5785条查询结果,搜索用时 468 毫秒
101.
琼北火山区是中国的主要火山群之一。笔者应用HDS - 1型快速数字闪烁测氡仪对琼北火山群马鞍岭和雷虎岭段的火山及断裂活动性进行了勘测和研究 ,对荣山 -岭南断裂进行了重点测量 ,查明了该断裂的具体位置 ,研究了火山及断裂的气体释放特征。发现Rn(氡 ) ,Th(钍 )的变化与断裂构造有密切关系 ,在Ⅰ ,Ⅱ测线上Th ,Rn异常对断裂的反映相当好。根据Th ,Rn的展布特征和浓度变化比较深入地分析了断裂的活动性。在雷虎岭西南 ,荣山 -岭南断裂活动性最强 ,而且 ,自西北向东南断裂规模及活动性均有增强的趋势。此外 ,还对火山的活动性进行了讨论和分析 相似文献
102.
103.
104.
由于工程需要,对广梧高速公路(马安—河口段)的地震地质情况进行了考察,马安—河口路段所处大地构造性质为东南地洼区,穿越了三个次级构造分区:白土断陷、思劳断隆、云浮断隆。路段附近发育3条断裂:肇庆断裂、河口断裂和吴川—四会断裂。前两者为非活动断裂,后者为活动断裂且星北东向从思劳附近穿过,是未来5.0级地震发生地段,烈度可达Ⅵ度。但路段附近地震活动水平较低,仅发生过4以—5.0级地震4次,最大烈度为Ⅴ度。白诸立交、河口立交的地震地质环境稳定,思劳立交基本稳定,沿线不易产生滑坡与崩塌。 相似文献
105.
106.
中国大陆及其邻区强震活动与活动地块关系研究 总被引:16,自引:0,他引:16
从活动地块假说出发 ,在活动地块研究的基础上 ,探讨了中国大陆及邻区活动地块与强震活动的关系。研究指出 ,主要构造变形和强烈地震大都发生在活动地块边界。在占总面积 17%的活动地块边界上 ,集中了全部的 8级以上巨大地震和 86 %的 7级以上大地震 ,其释放能量占全部总能量的 95 %以上 ,表明中国大陆及其邻区活动地块边界带控制了绝大部分的强地震。从活动地块的整体来看 ,强震活动不仅显示出显著的韵律性特征 ,而且其高、低起伏基本上与中国大陆地区一致 ,只是强震活跃时段有时稍长于中国大陆。各轮回强震活动都有各自活动的主体地区 ,反映了不同活跃期内地块的不同活动方式。文中还从现今地壳运动角度 ,讨论了活动地块运动速率与强地震活动水平之间的可能联系。 相似文献
107.
Erkan Aydar Alain Gourgaud Inan Ulusoy Fabrice Digonnet Philippe Labazuy Erdal Sen Hasan Bayhan Turker Kurttas Arif Umit Tolluoglu 《Journal of Volcanology and Geothermal Research》2003,123(3-4):301-312
Mount Nemrut, an active stratovolcano in eastern Turkey, is a great danger for its vicinity. The volcano possesses a summit caldera which cuts the volcano into two stages, i.e. pre- and post-caldera. Wisps of smoke and hot springs are to be found within the caldera. Although the last recorded volcanic activity is known to have been in 1441, we consider here that the last eruption of Nemrut occurred more recently, probably just before 1597. The present active tectonic regime, historical eruptions, occurrence of mantle-derived magmatic gases and the fumarole and hot spring activities on the caldera floor make Nemrut Volcano a real danger for its vicinity. According to the volcanological past of Nemrut, the styles of expected eruptions are well-focused on two types: (1) occurrence of water within the caldera leads to phreatomagmatic (highly energetic) eruptions, subsequently followed by lava extrusions, and (2) effusions–extrusions (non-explosive or weakly energetic eruptions) on the flanks from fissures. To predict the impact area of future eruptions, a series of morphological analyses based on field observations, Digital Elevation Model and satellite images were realized. Twenty-two valleys (main transport pathways) were classified according to their importance, and the physical parameters related to the valleys were determined. The slope values in each point of the flanks and the Heim parameters H/L were calculated. In the light of morphological analysis the possible impact areas around the volcano and danger zones were proposed. The possible transport pathways of the products of expected volcanic events are unified in three main directions: Bitlis, Guroymak, Tatvan and Ahlat cities, the about 135 000 inhabitants of which could be threatened by future eruptions of this poorly known and unsurveyed volcano. 相似文献
108.
The Milos volcanic field includes a well-exposed volcaniclastic succession which records a long history of submarine explosive
volcanism. The Bombarda volcano, a rhyolitic monogenetic center, erupted ∼1.7 Ma at a depth <200 m below sea level. The aphyric
products are represented by a volcaniclastic apron (up to 50 m thick) and a lava dome. The apron is composed of pale gray
juvenile fragments and accessory lithic clasts ranging from ash to blocks. The juvenile clasts are highly vesicular to non-vesicular;
the vesicles are dominantly tube vesicles. The volcaniclastic apron is made up of three fades: massive to normally graded
pumice-lithic breccia, stratified pumice-lithic breccia, and laminated ash with pumice blocks. We interpret the apron beds
to be the result of water-supported, volcaniclastic mass-How emplacement, derived directly from the collapse of a small-volume,
subaqueous eruption column and from syn-eruptive, down-slope resedimentation of volcaniclastic debris. During this eruptive
phase, the activity could have involved a complex combination of phreatomagmatic explosions and minor submarine effusion.
The lava dome, emplaced later in the source area, is made up of flow-banded lava and separated from the apron by an obsidian
carapace a few meters thick. The near-vertical orientation of the carapace suggests that the dome was intruded within the
apron. Remobilization of pyroclastic debris could have been triggered by seismic activity and the lava dome emplacement.
Published online: 30 January 2003
Editorial responsibility: J. McPhie 相似文献
109.
Jean-Louis Le Mouël Pierre-Noël Mayaud Peter Shebalin 《Comptes Rendus Geoscience》2003,335(13):935-941
Big perturbations of the magnetic field (amplitudes larger than 250 nT) are simply detected by subtracting the values of a model from the measurements of CHAMP satellite. Taking a full year of CHAMP data and organizing them in four subsets of three months length (spring, summer, autumn, winter), it is found that: (a) the two domains where such big perturbations mainly exist are limited, in both hemispheres, by a parallel of high latitude of the corrected geomagnetic coordinates system; (b) a conspicuous seasonal (annual) variation affects the density of the perturbations and is opposite in the two hemispheres. We hold that these perturbations are linked to the midday magnetic activity within the auroral zone, long ago described by one of us (Mayaud, 1956). The source of the perturbations observed at the satellite altitude would be field-aligned currents resulting from the penetration of the solar wind into the magnetospheric cusps. To cite this article: J.-L. Le Mouël et al., C. R. Geoscience 335 (2003). 相似文献
110.
Rockfall susceptibility has been analysed in mountain cliffs of the Cantabrian Range, North Spain. The main aim of this analysis has been to build a predictive model of rockfall activity from a low number of environmental and geological variables. The rockfall activity has been quantified in a GIS. The cartographic information used shows the spatial distribution of all the recent talus screes as well as their associated source areas in the rock-slopes. The area relation At/Ar (recent talus scree polygon/source basins) in the rock slopes has been used as the rockfall activity indicator. This relation has been validated in 50 pilot rock-slopes and compared with the relation number of recent rock fragments/source basin, obtained from field work. The environmental factors causing rockfall depend on the rock slope situation, and these are: altitude and sun radiation on the rock cliff. The geological factors considered are: lithology, relative position of the main discontinuities with respect to the topographic surface and two morphologic parameters: the roughness and slope gradient. A logistic regression analysis has been applied to a population of 442 limestone and quartzite rock cliffs. The dependent variable is the rockfall activity indicator, which allows the definition of two classes of rock cliff units: low and high activity. The independent variables are altitude, sun radiation (equinox radiation, summer solstice radiation, winter solstice radiation), slope roughness, slope gradient,anisotropy and lithology. Results suggest that it is possible tobuild a valid cartographic predictive model for rockfall activity in mountain rock cliffs from a limited number of easily obtainable variables. The method is especially applicable in massive rock slopes or in regions with uniform rock mass characteristics. 相似文献