全文获取类型
收费全文 | 52827篇 |
免费 | 9445篇 |
国内免费 | 12599篇 |
专业分类
测绘学 | 3503篇 |
大气科学 | 11435篇 |
地球物理 | 13373篇 |
地质学 | 25527篇 |
海洋学 | 6006篇 |
天文学 | 2454篇 |
综合类 | 5984篇 |
自然地理 | 6589篇 |
出版年
2024年 | 174篇 |
2023年 | 684篇 |
2022年 | 2111篇 |
2021年 | 2459篇 |
2020年 | 2049篇 |
2019年 | 2382篇 |
2018年 | 2815篇 |
2017年 | 2542篇 |
2016年 | 2977篇 |
2015年 | 2509篇 |
2014年 | 3092篇 |
2013年 | 3036篇 |
2012年 | 2904篇 |
2011年 | 2976篇 |
2010年 | 3127篇 |
2009年 | 3071篇 |
2008年 | 2808篇 |
2007年 | 2704篇 |
2006年 | 2164篇 |
2005年 | 1961篇 |
2004年 | 1573篇 |
2003年 | 1586篇 |
2002年 | 1495篇 |
2001年 | 1522篇 |
2000年 | 1835篇 |
1999年 | 2652篇 |
1998年 | 2159篇 |
1997年 | 2060篇 |
1996年 | 1896篇 |
1995年 | 1664篇 |
1994年 | 1500篇 |
1993年 | 1328篇 |
1992年 | 1058篇 |
1991年 | 833篇 |
1990年 | 609篇 |
1989年 | 570篇 |
1988年 | 509篇 |
1987年 | 305篇 |
1986年 | 267篇 |
1985年 | 188篇 |
1984年 | 156篇 |
1983年 | 121篇 |
1982年 | 121篇 |
1981年 | 98篇 |
1980年 | 56篇 |
1979年 | 55篇 |
1978年 | 20篇 |
1977年 | 14篇 |
1976年 | 12篇 |
1958年 | 43篇 |
排序方式: 共有10000条查询结果,搜索用时 564 毫秒
851.
Midstream of the Keelung River Basin in Northern Taiwan has become highly urbanized and densely populated area. Flood inundation
along riversides frequently occurred during typhoons or rainstorms. Three protection measures, including constructions of
high-level protection levees, a diversion channel, and a detention reservoir, were proposed for flood mitigation. The main
purpose of this study is to evaluate the flood mitigation performance of the three proposed structural measures by using combined
hydrologic analyses and hydraulic routings. A semi-distributed parallel-type linear reservoirs rainfall-runoff model was used
for estimating the surface runoff. Furthermore, a 1-D dynamic channel routing model was coupled with a two-dimensional inundation
model to simulate the hydraulic characteristics of river flooding and overland flow. Simulation results of flood stages, runoff
peak discharges, and inundation extent under design rainfall scenarios were chosen as the criteria for evaluation. The results
showed a diversion channel is superior to the other two measures for flood mitigation of the study area. After the process
of environmental impact assessment, a revised diversion channel approach has been approved for construction as the major structural
measure. 相似文献
852.
Construction techniques for the Taklamakan Desert Highway: research on the construction materials and the results of field tests 总被引:1,自引:0,他引:1
After conducting many laboratory and field experiments, several key technical issues related to the construction of China’s
Taklamakan Desert Highway have been satisfactorily resolved. In particular, considerable progress has been made on the dry
compaction of a sand sub-base, road design parameters, the creation of a structure that combines a sub-grade and asphalt pavement,
analysis of the stability of a sand sub-base strengthened with geotextiles, and on the development of a complete set of construction
techniques. The achievements of this research were successfully applied for the first time in the Taklamakan Desert, where
the environmental conditions are extremely harsh. The results suggest that the construction of this highway was economical
and that the simple construction methods produced a reliable highway. The resulting highway is believed to be the world’s
first long-distance graded highway running through a huge desert with migrating dunes. 相似文献
853.
1 IntroductionThe Mesozoic-Cenozoic tectonic evolution and ki-netics mechanism of the intracontinental orogen are thekey subjects of continental dynamics (Ma Zongjin andGao Xianglin, 2004) and the key to understanding theregional geological tectonics (Qia… 相似文献
854.
1 IntroductionFracturing plays an important role in increasingthe production and injection and enhancing the final re-covery of oil and gas. At present, the use of ahydroxypropyl guar gum, borate-crosslinked, hydraulicfracturing fluid systemhas become ext… 相似文献
855.
1IntroductionQuite a number of porphyry copper deposits havebeen found in the Cenozoic alkali-intrusions along theJinshajiang-Ailaoshan-Red River fault zone,whichconstitute the Cenozoic ore belt in China.The Cenozo-ic alkali-intrusive rocks are similar in… 相似文献
856.
1 Introduction Alunite [KAl3(SO4)2(OH)6] is a very important non-ferrous metal resource, so many countries throughout the world have made great investments in research on the mechanism of its formation, its geological characteristics and applications. O… 相似文献
857.
858.
提出快速获得航空影像并及时制作DOM、DLG的一种手段.介绍遥控飞艇数字摄影系统的工作原理,探讨存在的问题. 相似文献
859.
张赤军 《武汉大学学报(信息科学版)》2005,30(6):471-473
介绍了大地水准面(N)与似大地水准面(ξ)之差公式的推导方法,揭示了其物理内涵,论述了其在精化大地水准面中的重要作用。当似大地水准面精度达到cm级时,大地水准面也将达到同样的精度。 相似文献
860.
数据模型是GIS的灵魂和关键,为了使开发出的GIS尽可能准确地反映地理空间,能够较好地满足GIS用户各方面的需要,而网络拓扑对网络的构成也至关重要,本文分析和总结了早期和近期GIS几种数据模型的优缺点,并在此基础上提出了整体GIS数据模型及网络设计的几种常见模式. 相似文献