全文获取类型
收费全文 | 519篇 |
免费 | 89篇 |
国内免费 | 67篇 |
专业分类
测绘学 | 39篇 |
大气科学 | 96篇 |
地球物理 | 178篇 |
地质学 | 192篇 |
海洋学 | 97篇 |
天文学 | 9篇 |
综合类 | 5篇 |
自然地理 | 59篇 |
出版年
2023年 | 2篇 |
2022年 | 14篇 |
2021年 | 16篇 |
2020年 | 9篇 |
2019年 | 30篇 |
2018年 | 8篇 |
2017年 | 23篇 |
2016年 | 23篇 |
2015年 | 24篇 |
2014年 | 36篇 |
2013年 | 35篇 |
2012年 | 19篇 |
2011年 | 32篇 |
2010年 | 25篇 |
2009年 | 29篇 |
2008年 | 50篇 |
2007年 | 28篇 |
2006年 | 36篇 |
2005年 | 29篇 |
2004年 | 17篇 |
2003年 | 16篇 |
2002年 | 26篇 |
2001年 | 10篇 |
2000年 | 12篇 |
1999年 | 17篇 |
1998年 | 15篇 |
1997年 | 13篇 |
1996年 | 19篇 |
1995年 | 10篇 |
1994年 | 12篇 |
1993年 | 13篇 |
1992年 | 8篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1988年 | 4篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有675条查询结果,搜索用时 302 毫秒
141.
D.R. Bridgland R. Westaway A.J. Howard A.J. Long M.J. White 《Proceedings of the Geologists' Association. Geologists' Association》2010,121(2):113-127
In recent years it has been demonstrated that the formation of long-timescale river terrace sequences, which are generally found in areas beyond the extent of most if not all of the Middle and Late Pleistocene ice sheets, has invariably been a response to uplift during the Late Cenozoic and especially the Quaternary. Climatic fluctuation at a Milankovitch timescale has driven the alternations of aggradation and incision recorded in such terraces. It has been widely observed, however, that fluvial terraces also occur in areas glaciated during the Last Glacial Maximum (LGM), which coincides with marine oxygen isotope stage (MIS) 2. This paper, in seeking to compare records from inside and outside of the LGM ice limit, concentrates on a single English river system, that of the Humber. The Humber estuary is shared by the largely Pennine-derived drainage of the Yorkshire Ouse, to the north and entirely within the MIS 2 glacial limit, and, to the south, the Trent, which is almost wholly outside the LGM limit. Thus the Trent has a terrace sequence extending back to the Middle Pleistocene, whereas in the component rivers of the Ouse system, records begin with the melting of the last glacial ice. Importantly, there is considerable difference in the disposition of the post-LGM fluvial deposits in these two subsystems. In the Ouse system there are modest terrace staircases, commencing with full glacial deposits that stand up to 30 m above the modern floodplain. In the Trent, in contrast, last glacial gravels form the foundation of the modern floodplain, with Holocene sediments emplaced directly above them. Thus there is little or no post-LGM incision in the Trent, whereas in the Ouse several incision events are recorded, continuing into the later stages of the Holocene. Wider comparison reveals that the Ouse system is an exemplar for other sequences within the MIS 2 limit, whereas systems beyond this glaciation typically have last glacial sediments beneath their modern floodplains and show little evidence of Holocene incision. The various possible explanations of these differences are discussed, with emphasis placed on glacio-isostatic uplift of areas glaciated during MIS 2 as the main reason for the significant post-glacial incision that typifies valleys in such regions. A new approach to modelling glacio-isostatic adjustment is outlined, from which it is concluded that lower-crustal flow plays a significant role in this process in regions of relatively hot and dynamic crust, like northern England, in addition to the mantle flow that is considered in conventional analyses of glacio-isostasy. Lower-crustal flow has a significant effect due to the combination of the small spatial scale of the glaciated region of northern England and the high mobility of the lower-crustal layer beneath it, due to the heating effect of the widespread Palaeozoic granite in the area. 相似文献
142.
143.
Neil F. Glasser Philip D. Hughes Cassandra Fenton Christoph Schnabel Henrik Rother 《第四纪科学杂志》2012,27(1):97-104
This paper presents results of the analysis of paired cosmogenic isotopes (10Be and 26Al) from eight quartz‐rich samples collected from ice‐moulded bedrock on the Aran ridge, the highest land in the British Isles south of Snowdon. On the Aran ridge, comprising the summits of Aran Fawddwy (905 m a.s.l.) and Aran Benllyn (885 m a.s.l.), 26Al and 10Be ages indicate complete ice coverage and glacial erosion at the global Last Glacial Maximum (LGM). Six samples from the summit ridge above 750–800 m a.s.l. yielded paired 10Be and 26Al ages ranging from 17.2 to 34.4 ka, respectively. Four of these samples are very close in age (10Be ages of 17.5 ± 0.6, 17.5 ± 0.7, 19.7 ± 0.8 and 20.0 ± 0.7 ka) and are interpreted as representing the exposure age of the summit ridge. Two other summit samples are much older (10Be ages of 27.5 ± 1.0 and 33.9 ± 1.2 ka) and these results may indicate nuclide inheritance. The 26Al/10Be ratios for all samples are indistinguishable within one‐sigma uncertainty from the production rate ratio line, indicating that there is no evidence for a complex exposure history. These results indicate that the last Welsh Ice Cap was thick enough to completely cover the Aran ridge and achieve glacial erosion at the LGM. However, between c. 20 and 17 ka ridge summits were exposed as nunataks at a time when glacial erosion at lower elevations (below 750–800 m a.s.l.) was achieved by large outlet glaciers in the valleys surrounding the mountains. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
144.
末次冰期东亚季风气候的数值模拟研究 总被引:3,自引:0,他引:3
利用一个T42全球大气环流谱模式模拟了现代及末次冰期极盛时期边界条件下的东亚季风气候,并与中国区域内古气候变化的地质证据了对比,综合分析表明,末次末期时东亚冬季风强盛,夏季风衰退,气候大陆度增加。年平均气温普遍下降,我国华南,西北东部至华北,东北地区分别比现代降温2-4℃、8-10℃及10℃以上;季风多降水明显减少,与现代相比,东南沿海,江淮至华北,东北地区年降水量分别减少70-80%,60-70 相似文献
145.
12 severe rainstorms have been experienced by different meteorological sub-divisions of Maharashtra State during the last 100-year period from 1891-1990. For each of the rainstorms efficiency factors (i.e. P/ M ratios) were worked out for maximum one-day duration and for three standard areas of 1000, 5000, and 10,000 km2. Comparison of these ratios with the past has shown that the most efficient rainstorm over Maharashtra was the rainstorm of June, 1908 over the Vidarbha region whose full DAD data as well as isohyetal pattern have been given. 相似文献
146.
对核电厂选址的工程地震工作中常见的术语:地震区、地震带、潜在震源区、地震构造区和地震危险区的含义及其相互关系进行了讨论,并结合HAF0101法规对地震构造区最大潜在地震的评价提出见解 相似文献
147.
STANLEY N.DEMING JOHN A.PALASOTA Department of Chemistry University of Houston Houston TX - U.S.A.AND JOHN M.NOCERINO United States Environmental Protection Agency Environmental Monitoring Systems Laboratory Las Vegas NV - U.S.A. Author to whom correspondence should be addressed. 《地理学报(英文版)》1993,(5)
The geometric properties of three common object-preprocessing transformations(constant sum,orclosure;constant length,or normalization;and maximum value,or ratioing)are investigated.Anargument is made for using absolute values in the constant sum and maximum value transformations.In general,each transformation distorts the shape and dimensionality of patterns in the data:transformed data lie on(C-l)-dimensional surfaces in the original C-dimensional space.A data set thathas been closed by one of these transformations can be reopened if a vector containing the constant sums,constant lengths or maximum values of the original objects was retained.Transformed data sets may befreely interconverted among these three transformations without the loss of information. 相似文献
148.
149.
150.
台湾集集和华北大同地震序列的定量模型分析 总被引:4,自引:0,他引:4
介绍了传染型余震序列(ETAS)模型的基本原理和发展概况,并利用该模型分析了1999年开始的台湾集集地震序列(主震Ms7.6)和1989年开始的大同地震序列(主震为Ms5.7)。通过分析计算,得到了二个序列的ETAS参数向量,并结合各自的孕震环境和机制分析了二个地震序列的异同和序列衰减规律。 相似文献