全文获取类型
收费全文 | 1240篇 |
免费 | 271篇 |
国内免费 | 317篇 |
专业分类
测绘学 | 184篇 |
大气科学 | 266篇 |
地球物理 | 285篇 |
地质学 | 639篇 |
海洋学 | 202篇 |
天文学 | 35篇 |
综合类 | 98篇 |
自然地理 | 119篇 |
出版年
2024年 | 10篇 |
2023年 | 25篇 |
2022年 | 75篇 |
2021年 | 91篇 |
2020年 | 94篇 |
2019年 | 86篇 |
2018年 | 90篇 |
2017年 | 70篇 |
2016年 | 78篇 |
2015年 | 76篇 |
2014年 | 75篇 |
2013年 | 90篇 |
2012年 | 116篇 |
2011年 | 103篇 |
2010年 | 61篇 |
2009年 | 94篇 |
2008年 | 65篇 |
2007年 | 56篇 |
2006年 | 45篇 |
2005年 | 29篇 |
2004年 | 26篇 |
2003年 | 29篇 |
2002年 | 29篇 |
2001年 | 29篇 |
2000年 | 33篇 |
1999年 | 37篇 |
1998年 | 24篇 |
1997年 | 31篇 |
1996年 | 18篇 |
1995年 | 23篇 |
1994年 | 20篇 |
1993年 | 18篇 |
1992年 | 19篇 |
1991年 | 12篇 |
1990年 | 8篇 |
1989年 | 13篇 |
1988年 | 8篇 |
1987年 | 1篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 8篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 2篇 |
排序方式: 共有1828条查询结果,搜索用时 984 毫秒
21.
22.
Zheng Feili Tang Keli Zhang Keli Cha Xuan Bai Hongying Northwest Institute of Soil Water Conservation CAS Ministry of Water Resources Yangling Shaanxi People''s Republic of China 《地理学报(英文版)》1997,(2)
Forlongtime,theproblemaboutnaturalerosionandartificiallyacceleratederosionisindispute.HistoricalgeographersconsiderthathumaninducedecoenvironmentaldestructionisaccountablefortheseveresoilerosionandecoenvironmentdeteriorationonLoessPlateau[7,8].Somegeolog… 相似文献
23.
中国察尔汗钾盐矿床是在开发柴达木盆地进程中由筑路工人提供线索,1956年,化工部派员初步确定,1957年“中国科学院盐湖科学考查队”进行初步评价得以证实的。首次发现的钾盐是一种人工盐坑中新生的含钾光卤石矿物 相似文献
24.
25.
利用1960~1999年全国600个站月平均降水资料,对黄河三门峡水库—小浪底水库间的夏季降水总量年际变化进行了统计分析,并应用功率谱诊断方法提取了夏季各月降水的振荡周期。在此基础上,选取了黄河三门峡水库—小浪底水库间降水量多与少的年份,利用NCEP再分析资料研究了其上空的水汽变化以及水汽输送量变化。结果表明,黄河三门峡水库—小浪底水库间降水量多的年份,其上空为较为明显的水汽辐合;降水量比较少的年份,其上空为明显的水汽辐散。选取多雨年(1982年)及少雨年(1997年),结合NCEP再分析资料以及TBB资料,进一步验证了上述结论。 相似文献
26.
This paper deals with an analysis method for the response and motion of soil-like rigid-plastic bodies under seismic loading conditions. A continuity condition to determine the acceleration distribution within the rigid-plastic body when the failure occurs during seismic motions is proposed. Combining this continuity condition of acceleration and the ‘Generalized Limit Equilibrium Method (GLEM)’, the responses of the earth structure during seismic motions as well as the permanent displacements can be obtained, where GLEM is one of the limit equilibrium methods proposed by the authors for static problems and providing the approximate solution for Kötter's equation. The theoretical formulation of the method, the illustrative examples, and some comparisons between the analytical and experimental results are demonstrated. 相似文献
27.
文章通过广西右江百色水利枢纽地下发电厂房进水口与尾水洞高边坡的治理,介绍在此工程中具有特殊性的一些施工方法。该工程地质体为弱风化硅质泥岩夹泥化夹层、强风化含洞穴硅质泥岩石、强风化硅质岩及全强风化辉绿岩,地质条件非常复杂,对坡体的稳定极其不利。根据三维有限元的分析计算和国内有关权威专家的调查研究需施工1500kN、1000kN的锚索方能保证坡体的永久稳定。大吨位的锚索需锚固在强风化岩土体上,锚索设计采用能提高锚固力的防腐型压力分散锚索。通过现场锚索基本试验,其锚固力完全能满足工程需要。为保证进水口总体施工的进度,在施工进水口约30m高的垂直壁上的锚索时,笔者采用了通常施工中较少采用的垂直壁悬吊式施工法,满足了水电站的整体施工进度和要求。 相似文献
28.
29.
Comparison of the effects of unidirectional and sign‐alternating temperature gradients on the sintering of ice spheres
下载免费PDF全文
![点击此处可从《水文研究》网站下载免费的PDF全文](/ch/ext_images/free.gif)
To simplify the complex snow structures that occur in nature, polycrystalline ice spheres were produced and arranged vertically to model the sintering process. By controlling the temperatures on both the top and bottom of the ice sphere array, the effect of upward and downward vapor transfers was examined. The evolution of the neck areas between ice spheres was observed using X‐ray computed microtomography. As frequently observed under the basal part of a snow layer and previous experiments of snow temperature gradient metamorphism, depth hoar structures were formed along neck areas and their formation was found to be directly related to the vapor transfer direction. To model the temperature gradient inversion that can be induced in nature by daily cycles of radiative heating and cooling, we also performed sign‐alternating temperature gradient experiments on the ice sphere arrays. The morphological evolution of the neck and the associated vapor transfer were examined through image analysis and 2D modeling. The final microstructures of the neck area turned out to be a symmetrical distribution of ice protrusions bridging neighboring ice spheres. 相似文献
30.
Spatial conflicts may occur when map data are displayed at a scale smaller than that of the source map. This study applies the displacement operator in cartographic generalization to resolve such spatial conflicts and to improve the clarity and legibility of map. The immune genetic algorithm (IGA) is used in this study for buildings displacement to solve conflicts. IGA is based on the genetic algorithm (GA) and employs the self‐adjusting mechanism of antibody concentration to enhance population diversity. Meanwhile, the elitism retention strategy is adopted in IGA to guarantee that the best individual (antibody) is not lost and destroyed in the next generation to strengthen convergence efficiency. The compared experiment between IGA and GA shows that the displacement result produced by IGA performs better than GA. Finally, in order to make the displaced map more attractive to cartographers, two constraints – the building alignment constraint and building tangent relation constraint – are applied in IGA to restrict the buildings’ displacement. The same experimental data are adopted to prove that the improved IGA is useful for maintaining the two constraints. 相似文献