全文获取类型
收费全文 | 514篇 |
免费 | 14篇 |
国内免费 | 6篇 |
专业分类
测绘学 | 12篇 |
大气科学 | 70篇 |
地球物理 | 93篇 |
地质学 | 159篇 |
海洋学 | 39篇 |
天文学 | 74篇 |
自然地理 | 87篇 |
出版年
2024年 | 2篇 |
2021年 | 9篇 |
2020年 | 9篇 |
2019年 | 9篇 |
2018年 | 10篇 |
2017年 | 13篇 |
2016年 | 10篇 |
2015年 | 11篇 |
2014年 | 12篇 |
2013年 | 24篇 |
2012年 | 20篇 |
2011年 | 29篇 |
2010年 | 28篇 |
2009年 | 34篇 |
2008年 | 25篇 |
2007年 | 23篇 |
2006年 | 25篇 |
2005年 | 21篇 |
2004年 | 19篇 |
2003年 | 21篇 |
2002年 | 18篇 |
2001年 | 12篇 |
2000年 | 12篇 |
1999年 | 14篇 |
1998年 | 15篇 |
1997年 | 5篇 |
1996年 | 7篇 |
1995年 | 9篇 |
1994年 | 9篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 11篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1988年 | 3篇 |
1987年 | 12篇 |
1986年 | 3篇 |
1985年 | 5篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 3篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 3篇 |
1976年 | 1篇 |
1970年 | 1篇 |
1965年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有534条查询结果,搜索用时 15 毫秒
41.
Turbidity currents descending the slopes of deep‐water extensional basins or passive continental margins commonly encounter normal‐fault escarpments, but such large‐magnitude phenomena are hydraulically difficult to replicate at small scale in the laboratory. This study uses advanced computational fluid dynamics numerical simulations to monitor the response of large, natural‐scale unconfined turbidity currents (100 m thick and 2000 m wide at the inlet gate) to normal‐fault topography with a maximum relief of nearly 300 m. For comparative purposes, the turbidity current is first released on a non‐faulted pristine slope of 1·5° (simulation model 1). The expanding and waxing flow bypasses the slope without recognizable deposition within the visibility limit of 8 vol.% sand grain packing. Similar flow is then released towards the tip (model 2) and towards the centre (model 3) of a normal‐fault escarpment. In both of these latter models, the sand carried by flow tends to be entrapped in four distinct depozones: an upslope near‐gate zone of flow abrupt expansion and self‐regulation; a flow‐transverse zone at the fault footwall edge; a flow‐transverse zone at the immediate hangingwall; and a similar transverse zone near the crest of the hangingwall counter‐slope, where some of the deposited sand also tends to be reshuffled to the previous zone by a secondary reverse underflow. The near‐bottom reverse flow appears to be generated on a counter‐slope of 1·1°, increased to 2·0° by deposition. The Kelvin–Helmholtz interface instability plays an important role by causing three‐dimensional fluctuations in the flow velocity magnitude and sediment concentration. The thick deposits of large single‐surge flows may thus show hydraulic fluctuations resembling those widely ascribed to hyperpycnal flows. The study indicates further that the turbiditic slope fans formed on such fault topographies are likely to be patchy and hence may differ considerably from the existing slope‐fan conceptual models when it comes to the spatial prediction of main sand depozones. 相似文献
42.
Rob Westaway 《第四纪科学杂志》2010,25(5):715-723
The ‘new glacial stratigraphy’ (NGS) of Britain postulates that deposits hitherto assigned to the Anglian glaciation in Marine Isotope Stage (MIS) 12 represent MIS 16, 12, 10 and 6. This controversial idea can be tested at Sidestrand in north Norfolk, where fossiliferous temperate‐stage deposits underlie the oldest and overlie the youngest of the glacial deposits. Previous work has considered biostratigraphy and amino acid dating of these temperate‐stage deposits, but did not achieve tight age constraint using the amino acid evidence alone. The total hydrolysable amino acid fraction in intra‐crystalline protein from Bithynia tentaculata opercula has previously been analysed for concentrations of serine and alanine. Statistical screening of these data gives alanine/serine ratios of 4.572 ± 0.114 for the Sidestrand Hall Member (beneath the glacial deposits) and 3.564 ± 0.091 for the Sidestrand Cliff Formation (overlying the glacial deposits). These ratios imply ages of MIS 13a and 11c, respectively, indicating the latest Cromerian and early Hoxnian interglacials and invalidating the NGS. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
43.
44.
45.
46.
47.
48.
Using the Haskell–Thomson transfer matrix approach, an analytical solution is obtained for SH wave amplification by multiple layers of Gibson soils (i.e. viscoelastic layers with linearly varying shear moduli). Amplification spectra for typical soil and basement rock properties are calculated. A comparison of the Gibson soil response with that obtained for homogeneous soil models shows generally stronger amplifications associated with the Gibson soil. 相似文献
49.
50.