全文获取类型
收费全文 | 129篇 |
免费 | 331篇 |
国内免费 | 34篇 |
专业分类
地球物理 | 5篇 |
地质学 | 454篇 |
海洋学 | 13篇 |
综合类 | 5篇 |
自然地理 | 17篇 |
出版年
2023年 | 2篇 |
2022年 | 24篇 |
2021年 | 25篇 |
2020年 | 18篇 |
2019年 | 13篇 |
2018年 | 21篇 |
2017年 | 20篇 |
2016年 | 21篇 |
2015年 | 26篇 |
2014年 | 30篇 |
2013年 | 37篇 |
2012年 | 34篇 |
2011年 | 42篇 |
2010年 | 30篇 |
2009年 | 31篇 |
2008年 | 17篇 |
2007年 | 19篇 |
2006年 | 13篇 |
2005年 | 7篇 |
2004年 | 5篇 |
2003年 | 6篇 |
2002年 | 4篇 |
2001年 | 6篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 1篇 |
1997年 | 4篇 |
1996年 | 9篇 |
1995年 | 3篇 |
1994年 | 3篇 |
1993年 | 3篇 |
1992年 | 8篇 |
1990年 | 3篇 |
1986年 | 1篇 |
1985年 | 1篇 |
排序方式: 共有494条查询结果,搜索用时 15 毫秒
71.
72.
73.
74.
75.
An inexpensive improvement to lightweight percussion coring systems is presented. Non-stretching lines are often required to facilitate core sampling in hundreds of metres of water, unfortunately such lines are usually negatively buoyant, which creates difficulties in keeping lightweight core assemblies upright while lowering through the water column. The addition of urethane closed-cell foam to the core head creates buoyancy that vertically stabilizes the coring assembly within the water column and prevents the core barrel from contacting the sediment-water interface non-vertically. 相似文献
76.
77.
Unconsolidated, flocculent sediments that are frequently resuspended by wind action are found in many shallow-water lakes. Collecting sediment/water interface cores in such lakes for paleolimnological study may be problematic because it is difficult to determine the depth to the water/sediment interface. Accurately determining this water depth is necessary to guarantee that a piston corer does not penetrate the sediments prior to the drive and to maximize the core length. A simple instrument constructed with inexpensive, readily available components is described. This infrared floc detector (IFD) is used to sense the increased optical density of unconsolidated sediments as the detector is lowered into a lake. The IFD, in effect, yields a precise as well as an accurate measure of water depth. The depth to the water/sediment interface can be measured with an accuracy of approximately 1 cm, provided surface waters are relatively calm. 相似文献
78.
79.
80.