全文获取类型
收费全文 | 1891篇 |
免费 | 372篇 |
国内免费 | 420篇 |
专业分类
测绘学 | 112篇 |
大气科学 | 394篇 |
地球物理 | 495篇 |
地质学 | 843篇 |
海洋学 | 292篇 |
天文学 | 80篇 |
综合类 | 193篇 |
自然地理 | 274篇 |
出版年
2024年 | 9篇 |
2023年 | 44篇 |
2022年 | 119篇 |
2021年 | 131篇 |
2020年 | 130篇 |
2019年 | 110篇 |
2018年 | 109篇 |
2017年 | 134篇 |
2016年 | 156篇 |
2015年 | 117篇 |
2014年 | 130篇 |
2013年 | 133篇 |
2012年 | 110篇 |
2011年 | 130篇 |
2010年 | 88篇 |
2009年 | 117篇 |
2008年 | 102篇 |
2007年 | 95篇 |
2006年 | 84篇 |
2005年 | 63篇 |
2004年 | 45篇 |
2003年 | 47篇 |
2002年 | 40篇 |
2001年 | 37篇 |
2000年 | 35篇 |
1999年 | 63篇 |
1998年 | 42篇 |
1997年 | 52篇 |
1996年 | 26篇 |
1995年 | 27篇 |
1994年 | 24篇 |
1993年 | 20篇 |
1992年 | 30篇 |
1991年 | 21篇 |
1990年 | 14篇 |
1989年 | 14篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 7篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1971年 | 1篇 |
1958年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有2683条查询结果,搜索用时 265 毫秒
101.
The role of eddies in solute transport and recovery in rock fractures: Implication for groundwater remediation 下载免费PDF全文
A better understanding of solute transport and retention mechanism in rock fractures has been challenging due to difficulty in their direct observations in microscale rough‐walled fractures. Six representative troughs in a rough‐walled fracture were selected for microscale observations of eddy formation with increasing flow velocity and its effect on spatiotemporal changes of solute concentration. This experimental study was enabled by a microscale visualization technique of micro particle image velocimetry. With increasing flow velocity (Re ≤ 2.86), no eddies were generated, and solutes along the main streamlines transported rapidly, whereas those near the wall moved slowly. A larger amount of solutes remained trapped at all troughs at Re = 2.86 than Re < 1. For Re = 8.57, weak eddies started to be developed at the troughs on the lee side, which little contributed to overall solute flushing in the fracture. Accordingly, a large of amount of water was needed for solute flushing. The flow condition of 1 < Re < 10, before a full development of eddies, was least favourable in terms of time and amount of remediation fluid required to reach a target concentration. After large eddies were fully developed at troughs on the lee side for Re = 17.13, solutes were substantially reduced by eddies with less amount of water. Fully developed eddies were found to enhance solute transport and recovery, as opposed to a general consensus that eddies trap and delay solutes. Direct inflow into troughs on the stoss side also made a great contribution to solute flushing out of the troughs. This study indicates that fully developed eddies or strong inflows at troughs are highly possible to form for Re > 10 and this flow range could be favourable for efficient remediation. 相似文献
102.
西秦岭北缘断裂带地震活动特征及近期发展趋势 总被引:1,自引:0,他引:1
本文讨论了西秦岭北缘断裂带在青藏高原东北部三次地震活动高潮幕和两次地震活动低潮幕中的作用和特点,以及地震活动的时空强特征和近期发展趋势。 相似文献
103.
104.
105.
106.
本文采用大量实际资料,阐述了常德市的地质构造特征,从第四系及新构造运动的特点论述了常德市不同地段工程地质稳定性的差异,对该市灼规划建设布局和防震、防洪等方面提出了一些新的看法和建议。 相似文献
107.
新疆绿柱石宝石辐照致色机制的吸收光谱研究 总被引:1,自引:0,他引:1
本文对新疆阿尔泰天然淡蓝、浅蓝宝石级绿柱石辐照前后及退火处理伴随着颜色改变的吸收光谱等进行了分析讨论,认为天然淡蓝、浅蓝色绿柱石经~(60)Co-γ辐照变成黄绿色,其原因主要归因于遂道中Fe~(2-)向Fe~(3+)的转变和八面体中Fe~(3+)和配位体O~(2-)的电荷转移。 相似文献
108.
109.
110.
An AMT-model,consisting of a trajectory model and a one-dimensional boundary layer model,is tested fortrajectories arriving in Taiyuan to study the possibility of using it in Taiyuan.The sensitivity of the model tothe different processes was studied.Some parameters of the model were modified for the purpose of forecast-ing in specific mountainous terrain and dry climate conditions.Results of examples which we have workedout for Taiyuan circumstances for the periods of July(summer)1985 and January(winter)1986,show that the12h runs of the AMT-model are able to reproduce(on historical data)the sounding of Taiyuan.The AMT-modelcontributes fruitfully to short-range weather forecasts(12—36h ahead)during periods of severe air pollution andwhen cold waves occur. 相似文献