全文获取类型
收费全文 | 4837篇 |
免费 | 847篇 |
国内免费 | 1201篇 |
专业分类
测绘学 | 600篇 |
大气科学 | 1135篇 |
地球物理 | 912篇 |
地质学 | 2662篇 |
海洋学 | 498篇 |
天文学 | 176篇 |
综合类 | 277篇 |
自然地理 | 625篇 |
出版年
2024年 | 20篇 |
2023年 | 71篇 |
2022年 | 101篇 |
2021年 | 154篇 |
2020年 | 165篇 |
2019年 | 222篇 |
2018年 | 128篇 |
2017年 | 216篇 |
2016年 | 239篇 |
2015年 | 267篇 |
2014年 | 329篇 |
2013年 | 312篇 |
2012年 | 266篇 |
2011年 | 300篇 |
2010年 | 250篇 |
2009年 | 299篇 |
2008年 | 299篇 |
2007年 | 384篇 |
2006年 | 312篇 |
2005年 | 284篇 |
2004年 | 259篇 |
2003年 | 229篇 |
2002年 | 225篇 |
2001年 | 188篇 |
2000年 | 194篇 |
1999年 | 177篇 |
1998年 | 169篇 |
1997年 | 160篇 |
1996年 | 116篇 |
1995年 | 78篇 |
1994年 | 83篇 |
1993年 | 89篇 |
1992年 | 66篇 |
1991年 | 54篇 |
1990年 | 35篇 |
1989年 | 38篇 |
1988年 | 34篇 |
1987年 | 14篇 |
1986年 | 15篇 |
1985年 | 7篇 |
1984年 | 8篇 |
1983年 | 8篇 |
1982年 | 6篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 1篇 |
排序方式: 共有6885条查询结果,搜索用时 31 毫秒
71.
D. Parcerisa D. Gmez-Gras A. Trav J.D. Martín-Martín E. Maestro 《Journal of Geochemical Exploration》2006,89(1-3):318
Fe and Mn occur in calcite cements depending on the oxidizing–reducing conditions of cementing waters, which may change according to depositional and diagenetic environments. In red beds, Mn and Fe are available from the ferruginous matrix. Thus, it is possible to know the oxidizing–reducing conditions of fluids that precipitated calcite as a function of Mn and Fe content in calcite cement. A detailed petrological (with special attention to cathodoluminescence) and geochemical analysis of these cements is a useful tool to constrain the diagenetic evolution of red beds and the history of the basin where they deposited. 相似文献
72.
73.
V. Piscopo M. Barbieri V. Monetti G. Pagano S. Pistoni E. Ruggi D. Stanzione 《Hydrogeology Journal》2006,14(8):1508-1521
A conceptual hydrogeological model of the Viterbo thermal area (central Italy) has been developed. Though numerous studies have been conducted on its geological, geochemical and geothermal features, there is no generalized picture defining the origin and yield of the hydrothermal system. These latter aspects have therefore become the objectives of this research, which is based on new hydrogeological and geochemical investigations. The geological setting results in the coexistence of overlapped interacting aquifers. The shallow volcanic aquifer, characterized by fresh waters, is fed from the area around the Cimini Mountains and is limited at its base by the semiconfining marly-calcareous-arenaceous complex and low-permeability clays. To the west of Viterbo, vertical upflows of thermal waters of the sulphate-chloride-alkaline-earth type with higher gas contents, are due to the locally uplifted carbonate reservoir, the reduced thickness of the semiconfining layer and the high local geothermal gradient. The hot waters (30–60°C) are the result of deep circulation within the carbonate rocks (0.5–1.8 km) and have the same recharge area as the volcanic aquifer. The upward flow in the Viterbo thermal area is at least 0.1 m3/s. This flow feeds springs and deep wells, also recharging the volcanic aquifer from below. 相似文献
74.
A local-scale model for temperature-dependence of water-retention curves may be applicable to large scales. Consideration of this temperature dependence is important for modeling unsaturated flow and transport in the subsurface in numerous cases. Although significant progress has been made in understanding and modeling this temperature effect, almost all the previous studies have been limited to small scales (on the order of several centimeters). Numerical experiments were used to investigate the possibility of extending a local-scale model for the temperature-dependence of water retention curves to large scales (on the order of meters). Temperature effects on large-scale hydraulic properties are of interest in many practical applications. Numerical experiment results indicate that the local-scale model can indeed be applicable to large-scale problems for special porous media with high air entry values. A typical porous medium of this kind is the porous tuff matrix in the unsaturated zone of Yucca Mountain, Nevada, the proposed geologic disposal site for national high-level nuclear wastes. Whether this finding can approximately hold for general cases needs to be investigated in future studies. 相似文献
75.
The degree to which dust emissions are controlled by geomorphic conditions, wind environments and land use was investigated using the dust storm frequency (DSF) and data from more than 300 meteorological stations throughout northern China. Our analysis showed that most dust emissions originated in gobi deserts that developed in piedmont alluvial fans of the Kunlun, Qilian and Helan mountains. Dust emissions are low from other gobi desert regions, such as the northern Gurbantunggut and eastern Taklimakan, where high vegetation coverage restrained dust emissions or where dust-size particles are not abundant after a long period of strong wind erosion. Sandy deserts with relatively high vegetation coverage or an extensive cover by mobile sands are not a major dust source. Although the highest dust emissions did not appear in regions with the highest wind energy, DSF trends in each region from 1960 to 2003 were closely related to local wind activity. DSF was low in regions with high levels of human activity, where the mean DSF from 1960 to 2003 did not exceed 4 days/year; even from the 1960s to the early 1970s, the period with the greatest DSF, frequency did not exceed 8 days/year, which indicates that extensive land use did not contribute to DSF. The low DSF in these areas might result from the fact that although land use could produce abundant fine soil fractions, vegetation coverage and soil moisture remained higher than in the gobi deserts of arid China, thereby decreasing dust-storm occurrence. 相似文献
76.
The relationship between depth, age and gravity in the oceans 总被引:2,自引:0,他引:2
77.
78.
79.
四川省康定县滑坡灾害发育特征与形成条件 总被引:3,自引:0,他引:3
康定县地处四川盆地西缘山地及青藏高原过渡地带。县域内地势险峻,地形切割强烈,地层与地质构造复杂,新构造运动强烈,地震活动频繁。加之降水充沛,致使山地灾害十分发育,其中滑坡灾害占山地灾害的38.32%。通过搜集资料及现场调查,概述了该县县域内滑坡灾害的分布;从行政区划、自然地理及灾害规模等3方面统计分析了滑坡灾害的发育现状;从地形地貌、地层岩性、地质构造、降雨、地震活动、人类工程活动等方面总结了滑坡灾害的形成条件,并提出防治对策与措施,力求有效地预防与减少滑坡灾害的发生。 相似文献
80.
福建省大田县广平含煤区推覆构造特征及找煤预测 总被引:1,自引:0,他引:1
通过对区内推覆构造及地层等的研究,认为广平含煤区推覆体下蕴藏着丰富的煤炭资源,童子岩组煤系地层埋藏深度主要受发育于童子岩组上部的F1、F2推覆断层控制,并圈定出煤炭资源预测前景较好的3个区作为煤炭勘查后备基地。 相似文献