全文获取类型
收费全文 | 1387篇 |
免费 | 204篇 |
国内免费 | 265篇 |
专业分类
测绘学 | 516篇 |
大气科学 | 31篇 |
地球物理 | 298篇 |
地质学 | 702篇 |
海洋学 | 125篇 |
天文学 | 41篇 |
综合类 | 100篇 |
自然地理 | 43篇 |
出版年
2023年 | 14篇 |
2022年 | 49篇 |
2021年 | 75篇 |
2020年 | 96篇 |
2019年 | 75篇 |
2018年 | 41篇 |
2017年 | 85篇 |
2016年 | 75篇 |
2015年 | 85篇 |
2014年 | 105篇 |
2013年 | 105篇 |
2012年 | 73篇 |
2011年 | 82篇 |
2010年 | 70篇 |
2009年 | 62篇 |
2008年 | 62篇 |
2007年 | 82篇 |
2006年 | 48篇 |
2005年 | 41篇 |
2004年 | 53篇 |
2003年 | 41篇 |
2002年 | 54篇 |
2001年 | 47篇 |
2000年 | 33篇 |
1999年 | 24篇 |
1998年 | 31篇 |
1997年 | 25篇 |
1996年 | 34篇 |
1995年 | 27篇 |
1994年 | 28篇 |
1993年 | 19篇 |
1992年 | 26篇 |
1991年 | 17篇 |
1990年 | 11篇 |
1989年 | 16篇 |
1988年 | 6篇 |
1987年 | 12篇 |
1986年 | 5篇 |
1985年 | 11篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1978年 | 1篇 |
1971年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有1856条查询结果,搜索用时 15 毫秒
71.
72.
基于LIDAR数据的建筑物轮廓提取 总被引:2,自引:0,他引:2
建筑物轮廓的准确提取是建筑物三维重建中最重要的一步。本文在研究已有建筑物轮廓提取方法的基础上,针对LIDAR离散的点云数据,提出了一种自动快速提取建筑物轮廓信息的方法。首先通过点云数据生成城市的数字表面模型(DSM)和数字地面模型(DTM)相减计算得出规则化的数字表面模型(nDSM),进而将地面点和非地面点进行分类;其次,考虑到地物的几何特性,提出一种8邻域搜索的方法对非地面点点云进行分割,得到建筑物表面点云;最后运用基于梯度图的边界跟踪的方法来获取建筑物的轮廓信息。实验表明:该方法能有效地提取建筑物轮廓。 相似文献
73.
74.
75.
76.
This paper studies the projectile electron loss cross sections of C3 + colliding with atomic hydrogen in the frame work of extended over-barrier model at intermediate velocities (25 keV/u--600 keV/u). The electron loss is calculated in terms of the interaction between the screened target nucleus and the active projectile electron and of the interaction between projectile electron and target electron. Compared with the convergent close-coupling calculations, screening and anti-screening calculations, this model satisfactorily reproduces the experimentally obtained energy dependence of the electron-impact ionisation cross sections and the single electron loss cross sections over the energy range investigated here. 相似文献
77.
The chemical potential of electrons in a strong magnetic field is investigated. It is shown that the magnetic field has only a slight effect on electron chemical potential when B<1011 T, but electron chemical potential will decrease greatly when B>1011 T. The effects of a strong magnetic field on electron capture rates for 60Fe are discussed, and the result shows that the electron capture sharply decreases because of the strong magnetic field. 相似文献
78.
Monthly sediment load and streamflow series spanning 1963–2004 from four hydrological stations situation in the main stem of the Yangtze River, China, are analysed using scanning t‐test and the simple two‐phase linear regression scheme. Results indicate significant changes in the sediment load and streamflow from the upper reach to the lower reach of the Yangtze River. Relatively consistent positive coherency relations can be detected between streamflow and sediment load in the upper reach and negative coherency in the middle and lower reaches. Interestingly, negative coherency is found mainly for larger time scales. Changes in sediment load are the result mainly of human influence; specifically, the construction of water reservoirs may be the major cause of negative coherency. Accentuating the human influence from the upper to the lower reach results in inconsistent correlations between sediment load and streamflow. Decreasing sediment load being observed in recent years has the potential to alter the topographical properties of the river channel and the consequent development and recession of the Yangtze Delta. Results of this study are of practical significance for river channel management and evaluation of the influence of human activities on the hydrological regimes of large rivers. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
79.
刘晶晶 《海洋学报(英文版)》2010,29(9)
The influences of electron screening (ES) and electron energy correction (EEC) are investigated by superstrong magnetic field (SMF). We also discuss in detail the discrepant factor between our results and those of Fushiki, Gudmundsson and Pethick (FGP) in SMF. The results show that SMF has only a slight effect on ES when B < 109 T on the surfaces of most neutron stars. Whereas for some magnetars, SMF influence ES greatly when B > 109 T . For instance, due to SMF the ES potential may be increased about 23.6% and the EEC may be increased about 4 orders of magnitude at ρ/μe = 1.0×106 mol/cm3 and T9 = 1. On the other hand, the discrepant factor shows that our results are in good agreement with FGP's when B < 109 T . But the difference will be increased with increasing SMF. 相似文献
80.