全文获取类型
收费全文 | 149篇 |
免费 | 7篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 10篇 |
地球物理 | 9篇 |
地质学 | 91篇 |
海洋学 | 15篇 |
天文学 | 3篇 |
自然地理 | 26篇 |
出版年
2016年 | 2篇 |
2015年 | 1篇 |
2014年 | 4篇 |
2013年 | 9篇 |
2012年 | 9篇 |
2011年 | 6篇 |
2010年 | 5篇 |
2009年 | 3篇 |
2008年 | 6篇 |
2007年 | 3篇 |
2006年 | 8篇 |
2005年 | 6篇 |
2004年 | 8篇 |
2003年 | 1篇 |
2002年 | 3篇 |
2001年 | 2篇 |
2000年 | 3篇 |
1999年 | 1篇 |
1998年 | 5篇 |
1997年 | 5篇 |
1996年 | 12篇 |
1995年 | 4篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 2篇 |
1991年 | 10篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1973年 | 1篇 |
1963年 | 1篇 |
排序方式: 共有157条查询结果,搜索用时 630 毫秒
41.
42.
Exposure age dating and Equilibrium Line Altitude reconstruction of an Egesen moraine in the Maritime Alps, Italy 总被引:1,自引:0,他引:1
PAOLO ROBERTO FEDERICI DARRYL E. GRANGER MARTA PAPPALARDO ADRIANO RIBOLINI MATTEO SPAGNOLO ANDREW J. CYR 《Boreas: An International Journal of Quaternary Research》2008,37(2):245-253
Four boulder samples from the Piano del Praiet frontal moraine in the Gesso della Barra Valley (Maritime Alps) have been 10 Be dated. The results give a weighted mean age of 11 340±370 (870) yr, constraining the frontal moraine to the Egesen glacial stadial, during the Younger Dryas cold phase. By applying the same 10 Be production rate to other Egesen moraines previously dated in the Alps, we obtain similar ages for all of them. This suggests a synchroneity of the Egesen deglaciation in the European Alps at the end of the Younger Dryas. From the palaeoshape of the Egesen glacier, reconstructed by means of geomorphological mapping, an Equilibrium Line Altitude depression (δELA) of −520 to −530 m, with respect to the present-day ELA, and of −260 to −320 m, with respect to the Little Ice Age ELA, has been calculated. Comparison with other Alpine sector δELAs indicates that the Maritime Alps experienced humid climatic conditions during the Younger Dryas. 相似文献
43.
Melt Generation by Plumes: A Study of Hawaiian Volcanism 总被引:18,自引:9,他引:9
The mantle plume underlying the Hawaiian Swell has been modellednumerically using a stationary steady axisymmetric plume undera solid conducting lid. A method of calculating the rate ofmelt production from the plume has been developed, and the totalmelt production rate, the residual depth anomaly and the geoidanomaly have been used to constrain the model. The plume hasa central potential temperature of 1558 ?C and the mechanicalboundary layer is 72 km thick. An average of 6?6% melting occursin a melt-producing region which has a vertical extent of 55km and a radial extent of 130 km to produce 0?16 km3/y of melt.A parameterization of melt composition has been developed thatis consistent with laboratory experiments, with models of MORBgeneration, and with primitive Hawaiian tholeiites containing 16% MgO. There is no evidence that the major and minor elementconcentrations in the source region of Hawaiian tholeiites differfrom those in the source region of MORB. The model is consistentwith the REE contents of Kilauean tholeiites if the source regionhas primitive REE contents. The viscosity of the low-viscositylayer is constrained to be 1016m2/s. 相似文献
44.
45.
46.
Cr-Saturation Arrays in Concentrate Garnet Compositions from Kimberlite and their Use in Mantle Barometry 总被引:2,自引:0,他引:2
The spinelgarnet transition in Cr/Al-enriched peridotiticbulk compositions is known from experimental investigationsto occur at 2070 kbar, within the pressure range sampledby kimberlites. We show that the Cr2O3CaO compositionsof concentrate garnets from kimberlite have maximum Cr/Ca arrayscharacterized by Cr2O3/CaO 0·960·81, andinterpret the arrays as primary evidence of chromitegarnetcoexistence in Cr-rich harzburgitic or lherzolitic bulk compositionsderived from depth within the lithosphere. Under Cr-saturatedconditions on a known geotherm, each Cr/Ca array implicitlydelineates an isobar inside a garnet Cr2O3CaO diagram.This simplification invites a graphical approach to calibratean empirical Cr/Ca-in-pyrope barometer. Carbonaceous chromitegarnetharzburgite xenoliths from the Roberts Victor kimberlite tightlybracket a graphitediamond constraint (GDC) located atCr2O3 = 0·94CaO + 5·0 (wt %), representing a pivotalcalibration corresponding to 43 kbar on a 38 mW/m2 conductivegeotherm. Additional calibration points are established at 14,17·4 and 59·1 kbar by judiciously projecting garnetcompositions from simple-system experiments onto the same geotherm.The garnet Cr/Ca barometer is then simply formulated as follows(in wt %):
- if Cr2O3 0·94CaO + 5, then P38 (kbar) = 26·9+ 3·22Cr2O3 3·03CaO, or
- if Cr2O3 <0·94CaO + 5, then P38 (kbar) = 9·2+ 36[(Cr2O3+ 1·6)/(CaO + 7·02)].
47.
Chemical Characteristics of Carbonaceous Aerosols During Dust Storms over Xi'an in China 总被引:1,自引:0,他引:1
Characterization of carbonaceous aerosols including CC (carbonate carbon), OC (organic carbon), and EC (elemental carbon) were investigated at Xi'an, China, near Asian dust source regions in spring 2002. OC varied between 8.2 and 63.7μgm^- 3, while EC ranged between 2.4 and 17.2 μ m^-3 during the observation period. OC variations followed a similar pattern to EC and the correlation coefficient between OC and EC is 0.89 (n=31). The average percentage of total carbon (TC, sum of CC, OC, and EC) in PM2.5 during dust storm (DS) events was 13.6%, which is lower than that during non-dust storm (NDS) periods (22.7%). CC, OC, and EC accounted for 12.9%, 70.7%, and 16.4% of TC during DS events, respectively. The average ratio of OC/EC was 5.0 in DS events and 3.3 in NDS periods. The OC-EC correlation (R^2=0.76, n=6) was good in DS events, while it was stronger (R^2=0.90, n=25) in NDS periods. The percentage of watersoluble OC (WSOC) in TC accounted for 15.7%, and varied between 13.3% and 22.3% during DS events. The distribution of eight carbon fractions indicated that local emissions such as motor vehicle exhaust were the dominant contributors to carbonaceous particles. During DS events, soil dust dominated the chemical composition, contributing 69% to the PM2.5 mass, followed by organic matter (12.8%), sulfate (4%), EC (2.2%), and chloride (1.6%). Consequently, CC was mainly entrained by Asian dust. However, even in the atmosphere near Asian dust source regions, OC and EC in atmospheric dust were controlled by local emission rather titan the transport of Asian dust. 相似文献
48.
ANDREW J. RUSSELL PHILIP M. MARREN 《Boreas: An International Journal of Quaternary Research》1998,27(4):231-242
This study provides an insight into the impact of probably the largest flood ever to have been identified in mainland Britain by examining new sedimentary evidence from the Auchteraw terrace, Fort Augustus, Scotland. Study of three sections reveals a succession consisting of: (1) sheet gravels; (2) large trough-shaped depressions infilled with cross-stratified sands and gravels; (3) smaller-scale, finer-grained cross-strata; and (4) sheet-like, occasionally channelized, bimodal sand and gravel beds. This study shows that both the sedimentology and morphology of the Auchteraw terrace are consistent with jökulhlaup deposition and reveal a greater variety of lithofacies types than identified in previous studies of jökulhlaups from ice-dammed lakes. The fine-grained nature of the sediment discussed in this study emphasizes the importance of sediment supply for the formation of distinctive jökulhlaup successions. The sedimentary evidence recorded here provides a valuable tool for the interpretation of the magnitude and frequency of proglacial meltwater flows associated with Pleistocene ice sheets worldwide. 相似文献
49.
ANDREW FINLAYSON NICK GOLLEDGE TOM BRADWELL DEREK FABEL 《Boreas: An International Journal of Quaternary Research》2011,40(3):536-554
Finlayson, A., Golledge, N., Bradwell, T. & Fabel, D. 2011: Evolution of a Lateglacial mountain icecap in northern Scotland. Boreas, Vol. 40, pp. 536–554. 10.1111/j.1502‐3885.2010.00202.x. ISSN 0300‐9483. Detailed geomorphological mapping of the Beinn Dearg massif, northern Scotland, was conducted to examine the maximum (Younger Dryas) extent, and earlier interstadial evolution, of an icecap that existed during the Lateglacial period (14.7–11.7 cal. ka BP). Landform evidence indicates a plateau icecap configuration during the Younger Dryas. The interpreted age is supported by new cosmogenic exposure ages and previously reported interstadial sediments beyond the icecap margin. The reconstructed Younger Dryas Beinn Dearg icecap covered 176 km2. Equilibrium line altitudes (ELAs) of ~570–580 m were calculated for the icecap as a whole. The empirically reconstructed icecap is compared with recent numerical model simulations. The two methods produce an icecap with a similar configuration; however, differences are apparent in the extent of eastern and western outlets (±1–5 km), and in the spatial variation of ELAs. Results suggest that the numerical simulation overestimates the western and underestimates the eastern icecap extent. We attempt to quantify these differences in terms of icecap mass balance and assess their possible causes. Geomorphological evidence for the pre‐Younger Dryas icecap configuration indicates that the Beinn Dearg massif remained an important source during earlier deglaciation. In contrast, the neighbouring Fannich mountains acted as an ‘unzipping’ zone, and were ice‐free on their northern side by the Allerød (Greenland Interstadial 1c to 1a). Deglaciation continued over the western Beinn Dearg plateau, with the possibility that glaciers remained in some central and eastern catchments prior to (Younger Dryas) icecap (re)growth. 相似文献
50.
Rare Earth Element Inversions and Percolation Models for Hawaii 总被引:2,自引:4,他引:2
A detailed study has been made of the evolution with time ofthe mantle source and degree of melting required to producea typical Hawaiian volcano. The preshield stage involves a changefrom a depleted to a primitive mantle source and an increasein the melt fraction. Important intra- and inter-volcano variationsoccur during the shield stage which may be related to melt transportprocesses. With time, Mauna Loa's lavas show depletion in increasinglycompatible elements, a result which is consistent with percolationprocesses. Postshield magmas are generated by very small degreesof melting of a depleted mantle source and may be importantin the development of posterosional volcanism. Posterosionallavas can be generated by variable degrees of melting of anamphibole-bearing source that has been enriched by postshieldmagma. A simple percolation model is consistent with the isotopic evolutionof Hawaiian volcanoes. All of the observed isotopic variationseen between Hawaiian volcanoes may be produced from only twomantle sources by small variations in the percolation processes.
* Present address: Department of Earth Sciences, Parks Road, Oxford OX1 3PR, UK. 相似文献