全文获取类型
收费全文 | 2482篇 |
免费 | 457篇 |
国内免费 | 687篇 |
专业分类
测绘学 | 208篇 |
大气科学 | 532篇 |
地球物理 | 431篇 |
地质学 | 1744篇 |
海洋学 | 326篇 |
天文学 | 8篇 |
综合类 | 241篇 |
自然地理 | 136篇 |
出版年
2024年 | 11篇 |
2023年 | 40篇 |
2022年 | 60篇 |
2021年 | 68篇 |
2020年 | 70篇 |
2019年 | 100篇 |
2018年 | 76篇 |
2017年 | 128篇 |
2016年 | 120篇 |
2015年 | 115篇 |
2014年 | 184篇 |
2013年 | 128篇 |
2012年 | 179篇 |
2011年 | 174篇 |
2010年 | 158篇 |
2009年 | 186篇 |
2008年 | 153篇 |
2007年 | 187篇 |
2006年 | 182篇 |
2005年 | 158篇 |
2004年 | 126篇 |
2003年 | 127篇 |
2002年 | 117篇 |
2001年 | 106篇 |
2000年 | 96篇 |
1999年 | 83篇 |
1998年 | 66篇 |
1997年 | 87篇 |
1996年 | 75篇 |
1995年 | 41篇 |
1994年 | 63篇 |
1993年 | 46篇 |
1992年 | 37篇 |
1991年 | 28篇 |
1990年 | 18篇 |
1989年 | 13篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 4篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1954年 | 2篇 |
排序方式: 共有3626条查询结果,搜索用时 0 毫秒
221.
222.
223.
1 Introduction The landslides influences on the human society have become an environment difficult problem not able to be neglected, and according to the priority of harms, harms of landslides are only smaller than those from earthquakes in all sorts of natural hazards[1]. Landslide is part of rock mass, soil mass or their compound mass slides downward along a certain slid- ing surface under the actions of inner and external dy- namics, and it is one severe instability phenomenon of rock and s… 相似文献
224.
From the mid 1980s through the late 1990s, the channel of the lower Yellow River experienced serious shrinkage, which has decreased the flood conveyance of the channel and the sediment carrying capacity of the flow, raised the water levels of floods, and, thus, severely threatened the safety of flood control along the river. The completion of Xiaolangdi Dam in 1999 could help mitigate the channel shrinkage problem, but the situation has not changed yet. This paper analyses the characteristics, mechanisms, and conditions resulting in channel shrinkage, points out channel instabilities, and puts forward approaches of channel rehabilitation. 相似文献
225.
226.
在充分分析米脂—绥德岩盐田地质特征的基础上,对位于其中部的米脂姬家峁矿区O2m65亚段盐矿层赋存特征进行了研究,预测了矿区O2m65亚段岩盐资源储量,并对其开采条件进行了评价。 相似文献
227.
228.
曾绍炳 《华东地质学院学报》2007,30(1):51-54
在测量平差计算中,相当多的计算工作是矩阵转置、求逆、相乘等,人工解算容易出错,且现有各种平差软件一般均为过程隐含式的,不利于测量初学者掌握测量平差原理。探讨利用电子表格软件(Excel2003)的内置函数中的矩阵运算功能处理测量平差计算的方法,并以水准网条件平差的解算为例,介绍其使用方法及使用技巧,得到一些有益的结论。 相似文献
229.
230.
We develop and analyze a mixed finite element method for the solution of an elliptic system modeling a porous medium with
large cavities, called vugs. It consists of a second-order elliptic (i.e., Darcy) equation on part of the domain coupled to
a Stokes equation on the rest of the domain, and a slip boundary condition (due to Beavers–Joseph–Saffman) on the interface
between them. The tangential velocity is not continuous on the interface. We consider a 2-D vuggy porous medium with many
small cavities throughout its extent, so the interface is not isolated. We use a certain conforming Stokes element on rectangles,
slightly modified near the interface to account for the tangential discontinuity. This gives a mixed finite element method
for the entire Darcy–Stokes system with a regular sparsity pattern that is easy to implement, independent of the vug geometry,
as long as it aligns with the grid. We prove optimal global first-order L
2 convergence of the velocity and pressure, as well as the velocity gradient in the Stokes domain. Numerical results verify
these rates of convergence and even suggest somewhat better convergence in certain situations. Finally, we present a lower
dimensional space that uses Raviart–Thomas elements in the Darcy domain and uses our new modified elements near the interface
in transition to the Stokes elements. 相似文献