全文获取类型
收费全文 | 3153篇 |
免费 | 613篇 |
国内免费 | 1338篇 |
专业分类
测绘学 | 242篇 |
大气科学 | 107篇 |
地球物理 | 859篇 |
地质学 | 2936篇 |
海洋学 | 242篇 |
天文学 | 65篇 |
综合类 | 294篇 |
自然地理 | 359篇 |
出版年
2024年 | 10篇 |
2023年 | 26篇 |
2022年 | 99篇 |
2021年 | 124篇 |
2020年 | 149篇 |
2019年 | 200篇 |
2018年 | 169篇 |
2017年 | 156篇 |
2016年 | 188篇 |
2015年 | 199篇 |
2014年 | 228篇 |
2013年 | 243篇 |
2012年 | 248篇 |
2011年 | 247篇 |
2010年 | 236篇 |
2009年 | 245篇 |
2008年 | 210篇 |
2007年 | 269篇 |
2006年 | 231篇 |
2005年 | 187篇 |
2004年 | 172篇 |
2003年 | 154篇 |
2002年 | 137篇 |
2001年 | 139篇 |
2000年 | 123篇 |
1999年 | 93篇 |
1998年 | 96篇 |
1997年 | 101篇 |
1996年 | 76篇 |
1995年 | 50篇 |
1994年 | 71篇 |
1993年 | 46篇 |
1992年 | 44篇 |
1991年 | 32篇 |
1990年 | 23篇 |
1989年 | 25篇 |
1988年 | 15篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 7篇 |
1984年 | 4篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1954年 | 3篇 |
排序方式: 共有5104条查询结果,搜索用时 78 毫秒
101.
The occurrence of land subsidence in the Kingdom Saudi Arabia is either natural or man-made. Natural land subsidence occurs due to the development of subterranean voids by a solution of host rocks in carbonate and evaporite terrains, over many areas of Saudi Arabia. Man-induced land subsidence is either due to the removal of groundwater in the agricultural areas or to wetting of unstable soils. Therefore, earth fissures and a lowering of the ground surface in unconsolidated sediments took place in alluvial plains and volcanic vent terrains. Unstable soils include Sabkha soils and loess sediments. These types of soils occur in coastal plains, desert areas and volcanic terrains. When this soil is wetted either during agricultural activities, waste disposal or even during a rain storm, subsidence takes place due to either the removal of salts from the Sabkha soil or the rearrangement of soil particles in loess sediments. 相似文献
102.
Karst Hazard Assessment of Eastern Saudi Arabia 总被引:1,自引:0,他引:1
Karst phenomena exist in areas in the eastern part of Saudi Arabia, forming solution features such as sinkholes, collapsed dolines and solution caverns, as a result of the chemical leaching of the carbonate and evaporite formations by percolating water. The instability of these karst phenomena could produce land subsidence problems. This paper reviews the geology of documented karstic rock units in Saudi Arabia and proposes a simple engineering classification of the solution features characteristic of limestone. Two case histories in the Dhahran area, eastern Saudi Arabia, will be used as examples for the application of a modified engineering classification. 相似文献
103.
Oscillation and numerical dispersion limit the reliability of numerical solutions of the convection-dispersion equation when finite difference methods are used. To eliminate oscillation and reduce the numerical dispersion, an optimal upstream weighting with finite differences is proposed. The optimal values of upstream weighting coefficients numerically obtained are a function of the mesh Peclet number used. The accuracy of the proposed numerical method is tested against two classical problems for which analytical solutions exist. The comparison of the numerical results obtained with different numerical schemes and those obtained by the analytical solutions demonstrates the possibility of a real gain in precision using the proposed optimal weighting method. This gain in precision is verified by interpreting a tracer experiment performed in a laboratory column. 相似文献
104.
Yousheng Xu Hongsen Xie Jie Guo Haifei Zheng Yueming Zhang Maoshuang Song 《中国科学D辑(英文版)》1997,40(4):398-402
NaCI-H2O is the most fundamental ternary system in geology. Until now, the measurements of electrical conductivity of NaCl solutions
are still little at high pressures (> O.5 GPa) We measured the conductivity of 0.01 m NaCl solution at 0.4–5.0 GPa and 25-500°C.
The results are consistent with that of Quist and Marshall (1968) at 0.4 GPa. The conductivity of NaCl solution increases
with increasing temperature. The results also show that the conductivity of NaCl solution changes little with increasing pressure
below 1.5 GPa and changes rapidly with increasing pressure above 1.5 GPa. The rapid increase of the conductivity of NaCl solution
may play an important role in many geological processes (such as the genesis of ore deposits under hydrothermal condition)
and other fields.
Project supported by the National Natural Science Foundation of China. 相似文献
105.
106.
结合水化学的野外观测及室内计算,作者对桂林岩溶试验场、四川黄龙风景区和贵州乌江渡坝区3个岩溶动力系统的碳稳定同位素特征进行了分析,进而对系统的性质、系统中CO_2的来源、碳酸盐沉积过程中的碳同位素动力分馏、水化学和钙华的成因及热水钙华的~(14)C测年等地球化学问题作了探讨。结果表明,桂林岩溶试验场属于表层岩溶作用动力系统,其中的侵蚀动力主要来源于大气降水溶解土壤中的CO_2;四川黄龙风景区属于深部岩溶动力系统,侵蚀动力来自大气降水溶解幔源的CO_2;贵州乌江渡坝区岩溶系统,虽然属于表层岩溶动力系统,但其中一部分的同位素和水化学特征已受到人类活动的重大影响。 相似文献
107.
108.
借助辅助函数的思想, 采用波函数展开法给出了圆弧形凸起地形中隧洞对入射平面SH波影响问题的一个解析解.数值结果表明,凸起地形中隧洞的存在以及隧洞大小,对凸起地形表面运动,以及凸起地形中的隧洞的动应力集中均具有显著影响. 相似文献
109.
110.
大同煤田岩溶地下水的水文地质特征分析 总被引:1,自引:1,他引:1
根据大同煤田岩溶地下水化学特征资料、钻孔揭露岩溶发育的资料、以及矿井出水资料,结合岩溶地下水区域水文地质条件、岩溶地下水的水温与同位素特征,对大同煤田岩溶地下水的富水层位与找水方向作了进一步的探讨与分析。 相似文献