全文获取类型
收费全文 | 752篇 |
免费 | 60篇 |
国内免费 | 13篇 |
专业分类
测绘学 | 22篇 |
大气科学 | 114篇 |
地球物理 | 178篇 |
地质学 | 262篇 |
海洋学 | 76篇 |
天文学 | 101篇 |
综合类 | 1篇 |
自然地理 | 71篇 |
出版年
2022年 | 8篇 |
2021年 | 25篇 |
2020年 | 21篇 |
2019年 | 18篇 |
2018年 | 20篇 |
2017年 | 27篇 |
2016年 | 59篇 |
2015年 | 35篇 |
2014年 | 31篇 |
2013年 | 52篇 |
2012年 | 58篇 |
2011年 | 45篇 |
2010年 | 46篇 |
2009年 | 55篇 |
2008年 | 37篇 |
2007年 | 36篇 |
2006年 | 44篇 |
2005年 | 28篇 |
2004年 | 22篇 |
2003年 | 17篇 |
2002年 | 9篇 |
2001年 | 17篇 |
2000年 | 21篇 |
1999年 | 8篇 |
1998年 | 9篇 |
1997年 | 10篇 |
1996年 | 5篇 |
1995年 | 6篇 |
1994年 | 7篇 |
1993年 | 2篇 |
1992年 | 2篇 |
1991年 | 4篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 2篇 |
1985年 | 4篇 |
1984年 | 5篇 |
1983年 | 1篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 2篇 |
1979年 | 1篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1973年 | 1篇 |
1971年 | 1篇 |
1928年 | 1篇 |
1912年 | 1篇 |
排序方式: 共有825条查询结果,搜索用时 15 毫秒
821.
Evidence is presented to show that two measurable concentrations of microtephra particles can be detected in deposits of Late Devensian Late-glacial age in three sites in Scotland. One layer is attributed to the Vedde Ash, a marker horizon within the Younger Dryas chronozone. The second is a new tephra reported for the first time, which we name the Borrobol Tephra. This occurs consistently near the base of the Late-glacial Interstadial organic sediments at each site, and is thought to date to around 12.5 14C ka BP. Geochemical determinations using an electron microprobe confirm the identification of the Vedde Ash, suggest the Borrobol Tephra to have an Icelandic origin, and demonstrate the consistency of the geochemical signals at all three sites. © 1997 John Wiley & Sons, Ltd. 相似文献
822.
Architectural element analysis and detailed mapping of a 300 m along-strike exposure of the middle member Wood Canyon Formation, southern Marble Mountains, California, USA, provides new evidence for extensive braided–fluvial channel-belt deposits with adjacent overbank environments. Three-dimensional models constructed using ‘Structure from Motion’ techniques, combined with field-based observations, allowed interpretation of outcrop-scale trends, barforms, channel fills and fine-scale features. The ca 80 m thick member is divisible into five distinct units, including units M1 to M3 that form the bulk of the stratigraphy. Units are defined by stacking patterns of three facies associations (Facies Association 1 to Facies Association 3), each representing the product of a subenvironment within the fluvial system. In Facies Association 1, stacked cosets, interpreted as low-relief fluvial bars and channel fills, preserve vertical-accretion and downstream-accretion elements under unimodal north-north-west palaeoflow, with minor lateral accretion near bar edges. Deposits of Facies Association 2 to Facies Association 3, linked to overbank environments, are found only in unit M2, in the middle 27 m of the middle member. Floodplains, represented by Facies Association 2, include crumbly red-orange intervals of fine to medium-grained sandstone and thinner sets of cross-bedding than Facies Association 1, interbedded with thicker cross-stratification indicative of overbank splay or overland flow aggradation from adjacent channel belts during flood stage. Possible aeolian beds of Facies Association 3 preserve broad festooned trough cross-strata that average 23 cm in thickness; their small size, medium-grained sandstone and iron oxide cement suggest a high water table. The diverse assemblage of interpreted subenvironments, paired with bedform and facies patterns, implies a perennial fluvial system that gradually built large sand bars as the channel belt migrated and avulsed across an unconfined braided–fluvial reach, leaving the overbank area on its flanks subject to weathering and aeolian transport. Despite the occurrence of strata deposited in low-energy and ponded settings, and a marine influence proposed for nearby sections of middle member, no ichnofossils were encountered. 相似文献
823.
824.
A conceptual model of supra‐glacial lake formation on debris‐covered glaciers based on GPR facies analysis 下载免费PDF全文
Jordan R. Mertes Sarah S. Thompson Adam D. Booth Jason D. Gulley Douglas I. Benn 《地球表面变化过程与地形》2017,42(6):903-914
Supra‐glacial lakes and ponds can create hotspots of mass loss on debris‐covered glaciers. While much research has been directed at understanding lateral lake expansion, little is known about the rates or processes governing lake deepening. To a large degree, this knowledge gap persists due to sparse observations of lake beds. Here we report on the novel use of ground penetrating radar (GPR) surveys to simultaneously collect supra‐glacial lake bathymetry and bottom composition data from Spillway Lake (surface area of 2.4 × 105 m2; volume of 9.5 × 104 m3), which is located in the terminus region of the Ngozumpa Glacier in the Khumbu region of the Nepal Himalaya. We identified two GPR bottom signals corresponding to two sedimentary facies of (1) sub‐horizontal layered fine sediment drape and (2) coarse blocky diamict. We provide an understanding of the changes in subaqueous debris distribution that occur through stages of lake expansion by combining the GPR results with in situ observations of shoreline deposits matching the interpreted facies. From this, we present an updated conceptual model of supra‐glacial lake evolution, with the addition of data on the evolving debris environment, showing how dominant depositional processes can change as lakes evolve from perched lakes to multi‐basin base‐level lakes and finally onto large moraine‐dammed lakes. Throughout lake evolution, processes such as shoreline steepening, lakebed collapse into voids and conduit interception, subaerial and subaqueous calving and rapid areal expansion alter the spatial distribution and makeup of lakebed debris and sediments forcing a number of positive and negative feedbacks on lake expansion. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
825.