全文获取类型
| 收费全文 | 239篇 |
| 免费 | 23篇 |
| 国内免费 | 15篇 |
专业分类
| 测绘学 | 34篇 |
| 大气科学 | 2篇 |
| 地球物理 | 14篇 |
| 地质学 | 30篇 |
| 海洋学 | 190篇 |
| 综合类 | 5篇 |
| 自然地理 | 2篇 |
出版年
| 2023年 | 1篇 |
| 2022年 | 3篇 |
| 2021年 | 1篇 |
| 2020年 | 7篇 |
| 2019年 | 10篇 |
| 2018年 | 8篇 |
| 2017年 | 5篇 |
| 2016年 | 6篇 |
| 2015年 | 9篇 |
| 2014年 | 12篇 |
| 2013年 | 21篇 |
| 2012年 | 14篇 |
| 2011年 | 18篇 |
| 2010年 | 8篇 |
| 2009年 | 10篇 |
| 2008年 | 9篇 |
| 2007年 | 17篇 |
| 2006年 | 16篇 |
| 2005年 | 16篇 |
| 2004年 | 21篇 |
| 2003年 | 8篇 |
| 2002年 | 6篇 |
| 2001年 | 2篇 |
| 2000年 | 3篇 |
| 1999年 | 1篇 |
| 1998年 | 5篇 |
| 1997年 | 5篇 |
| 1996年 | 14篇 |
| 1995年 | 4篇 |
| 1994年 | 2篇 |
| 1993年 | 3篇 |
| 1992年 | 5篇 |
| 1991年 | 1篇 |
| 1990年 | 1篇 |
| 1989年 | 1篇 |
| 1988年 | 2篇 |
| 1987年 | 1篇 |
| 1954年 | 1篇 |
排序方式： 共有277条查询结果，搜索用时 187 毫秒
51.
52.
53.
54.
An experimental investigation on the initiation and development of bed forms on a bed of fine silica sand was conducted under alluvial flow conditions in a laboratory flume with a diverging channel. The main aims of the study were to assess： i） the steepness of bed forms in the transition stage of development; and ii） the threshold height of wavelets （ηt） that triggered the start of ripple development. Detailed bed profile measurements were carried out using an acoustic Doppler probe, traversed longitudinally over the sediment bed at various experimentation times. The bed form dimensions were extracted from such bed profile records and analysed for the wavelet, transition and equilibrium stages. It was found that the steepness of ripples in the transition and equilibrium stages were similar, confirming predictions of previous mathematical model simulations. A lognormal distribution fitted the wavelet length data. The wavelet threshold height was estimated as ηt ≈ 7 mm, or ηt≈ 80 in wall units. Such a height magnitude suggested that ripple development could be triggered by the wavelets reaching the outer flow zone of a turbulent boundary layer. The ηt value obtained corresponded generally to the intersection point between two predictive equations for bed form dimensions. A formulation was developed to predict ηt as a function of the sediment grain size, which was confirmed for the fine sand used in this study. 相似文献
55.
多波束声呐图像是进行海底底质分类的主要数据源之一,由于受海洋噪声、声波散射和混响、仪器设备等因素影响,其经各项常规改正后仍存在明显残差,突出表现在中央波束区和条带重叠区,难以形成高质量的声呐图像。文中分析了多波束声呐图像残差的成因及影响,提出了一种基于多条带最小二乘拟合的多波束声呐图像残差处理方法。首先,得到相邻声脉冲(ping)信号中央区域、重叠区域以及整体趋势的拟合函数;然后,通过拟合函数计算得到中央和重叠区域的残差改正系数;最后,通过改正系数进行残差改正。实验分析表明,该方法在保留原始细节的基础上,有效削弱了残差对声呐图像的影响,对多波束声呐图像处理具有参考和应用价值。 相似文献
56.
57.
The legacy of multiple marine transgressions is preserved in a complex morphology of ridges, mounds and reefs on the Carnarvon continental shelf, Western Australia. High-resolution multibeam sonar mapping, underwater photography and sampling across a 280 km2 area seaward of the Ningaloo Coast World Heritage Area shows that these raised features provide hardground habitat for modern coral and sponge communities. Prominent among these features is a 20 m high and 15 km long shore-parallel ridge at 60 m water depth. This ridge preserves the largely unaltered form of a fringing reef and is interpreted as the predecessor to modern Ningaloo Reef. Landward of the drowned reef, the inner shelf is covered by hundreds of mounds (bommies) up to 5 m high and linear ridges up to 1.5 km long and 16 m high. The ridges are uniformly oriented to the north-northeast and several converge at their landward limit. On the basis of their shape and alignment, these ridges are interpreted as relict long-walled parabolic dunes. Their preservation is attributed to cementation of calcareous sands to form aeolianite, prior to the post-glacial marine transgression. Some dune ridges abut areas of reef that rise to sea level and are highly irregular in outline but maintain a broad shore-parallel trend. These are tentatively interpreted as Last Interglacial in age. The mid-shelf and outer shelf are mostly sediment covered with relatively low densities of epibenthic biota and have patches of low-profile ridges that may also be relict reef shorelines. An evolutionary model for the Carnarvon shelf is proposed that relates the formation of drowned fringing reefs and aeolian dunes to Late Quaternary eustatic sea level. 相似文献
58.
59.
60.