全文获取类型
收费全文 | 247篇 |
免费 | 18篇 |
国内免费 | 4篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 36篇 |
地球物理 | 59篇 |
地质学 | 84篇 |
海洋学 | 28篇 |
天文学 | 35篇 |
自然地理 | 24篇 |
出版年
2022年 | 3篇 |
2021年 | 8篇 |
2020年 | 6篇 |
2019年 | 7篇 |
2018年 | 13篇 |
2017年 | 11篇 |
2016年 | 16篇 |
2015年 | 8篇 |
2014年 | 16篇 |
2013年 | 19篇 |
2012年 | 21篇 |
2011年 | 14篇 |
2010年 | 12篇 |
2009年 | 14篇 |
2008年 | 9篇 |
2007年 | 14篇 |
2006年 | 11篇 |
2005年 | 11篇 |
2004年 | 9篇 |
2003年 | 3篇 |
2002年 | 4篇 |
2001年 | 5篇 |
2000年 | 5篇 |
1999年 | 1篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 6篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 4篇 |
1991年 | 3篇 |
1988年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
1982年 | 4篇 |
1972年 | 1篇 |
排序方式: 共有269条查询结果,搜索用时 15 毫秒
161.
Remote rural areas have encountered significant change and the need for renegotiation of economic and social priorities in the late 20th and early 21st century. In our broader research, we ask how have such communities been responding to this change? What role have different organisations and agencies played? And, how have they acted on the aspirations of marginalised communities? In this paper we examine these issues through a case study of Westland District on the west coast of Aotearoa New Zealand's South Island. We probe the general shift towards prioritising tourism in the District, and highlight particular experiences in regard to Indigenous endeavour in tourism. We find that those engaged in leading local development and tourism have not collaborated strategically across the sector and have not established meaningful partnerships with the community that recognise both economic and socio‐cultural aspirations. 相似文献
162.
Dating very young planetary surfaces from crater statistics: A review of issues and challenges
下载免费PDF全文
![点击此处可从《Meteoritics & planetary science》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Jean-Pierre Williams Carolyn H. van der Bogert Asmin V. Pathare Gregory G. Michael Michelle R. Kirchoff Harald Hiesinger 《Meteoritics & planetary science》2018,53(4):554-582
Determining the ages of young planetary surfaces relies on using populations of small, often sub-km diameter impact craters due to the higher frequency at which they form. Smaller craters however can be less reliable for estimating ages as their size-frequency distribution is more susceptible to alteration with debate as to whether they should be used at all. With the current plethora of meter-scale resolution images acquired of the lunar and Martian surfaces, small craters have been widely used to derive model ages to establish the temporal relation of recent geologic events. In this review paper, we discuss the many factors that make smaller craters particularly challenging to use and should be taken into consideration when crater counts are confined to small crater diameters. Establishing confidence in a model age ultimately requires an understanding of the geologic context of the surface being dated as reliability can vary considerably and limitations of the dating technique should be considered in applying ages to any geologic interpretation. 相似文献
163.
Fiona J. Valesini Mathew Hourston Michelle D. Wildsmith Natasha J. Coen Ian C. Potter 《Estuarine, Coastal and Shelf Science》2010
This study has developed quantitative approaches for firstly classifying local-scale nearshore habitats in an estuary and then predicting the habitat of any nearshore site in that system. Both approaches employ measurements for a suite of enduring environmental criteria that are biologically relevant and can be easily derived from readily available maps. While the approaches were developed for south-western Australian estuaries, with a focus here on the Swan and Peel-Harvey, they can easily be tailored to any system. 相似文献
164.
Michelle S. Thompson Thomas J. Zega Jane Y. Howe 《Meteoritics & planetary science》2017,52(3):413-427
We report the results of the first dynamic, in situ heating of lunar soils to simulate micrometeorite impacts on the lunar surface. We performed slow‐ and rapid‐heating experiments inside the transmission electron microscope to understand the chemical and microstructural changes in surface soils resulting from space‐weathering processes. Our slow‐heating experiments show that the formation of Fe nanoparticles begins at ~575 °C. These nanoparticles also form as a result of rapid‐heating experiments, and electron energy‐loss spectroscopy measurements indicate the Fe nanoparticles are composed entirely of Fe0, suggesting this simulation accurately mimics micrometeorite space‐weathering processes occurring on airless body surfaces. In addition to Fe nanoparticles, rapid‐heating experiments also formed vesiculated textures in the samples. Several grains were subjected to repeated thermal shocks, and the measured size distribution and number of Fe nanoparticles evolved with each subsequent heating event. These results provide insight into the formation and growth mechanisms for Fe nanoparticles in space‐weathered soils and could provide a new methodology for relative age dating of individual soil grains from within a sample population. 相似文献
165.
The impact of the MJO on clusters of wintertime circulation anomalies over the North American region 总被引:1,自引:2,他引:1
Emily E. Riddle Marshall B. Stoner Nathaniel C. Johnson Michelle L. L’Heureux Dan C. Collins Steven B. Feldstein 《Climate Dynamics》2013,40(7-8):1749-1766
Recent studies have shown that the Madden–Julian Oscillation (MJO) impacts the leading modes of intraseasonal variability in the northern hemisphere extratropics, providing a possible source of predictive skill over North America at intraseasonal timescales. We find that a k-means cluster analysis of mid-level geopotential height anomalies over the North American region identifies several wintertime cluster patterns whose probabilities are strongly modulated during and after MJO events, particularly during certain phases of the El Niño-Southern Oscillation (ENSO). We use a simple new optimization method for determining the number of clusters, k, and show that it results in a set of clusters which are robust to changes in the domain or time period examined. Several of the resulting cluster patterns resemble linear combinations of the Arctic Oscillation (AO) and the Pacific/North American (PNA) teleconnection pattern, but show even stronger responses to the MJO and ENSO than clusters based on the AO and PNA alone. A cluster resembling the positive (negative) PNA has elevated probabilities approximately 8–14 days following phase 6 (phase 3) of the MJO, while a negative AO-like cluster has elevated probabilities 10–20 days following phase 7 of the MJO. The observed relationships are relatively well reproduced in the 11-year daily reforecast dataset from the National Centers for Environmental Prediction (NCEP) Climate Forecast System version 2 (CFSv2). This study statistically links MJO activity in the tropics to common intraseasonal circulation anomalies over the North American sector, establishing a framework that may be useful for improving extended range forecasts over this region. 相似文献
166.
Multiple datasets have demonstrated that the crust of Mars is fundamentally basaltic. However, spectral libraries used to interrogate thermal infrared spectra of Martian dark regions through spectral deconvolution have heretofore lacked mafic glasses despite the importance of amorphous phases (or phases with amorphous-like spectral signatures) in Martian mineralogy. To establish the presence and importance of basaltic-to-intermediate glasses in Martian lithologies, we created five such glasses, obtained their thermal infrared spectra and included the spectra in a library used to deconvolve nine regional Thermal Emission Spectrometer spectra from Mars. We employed the nonnegative least squares (NNLS) deconvolution method, which yields deconvolved phase abundances and the uncertainties associated with those abundances. The basaltic-to-intermediate glasses do not appear in the deconvolution solutions, indicating they are not globally or regionally important phases. Because Martian igneous or impact processes are capable of basaltic-to-intermediate glass formation, the lack of such glasses in the deconvolved mineralogies suggests either the glasses did not form in detectable quantities or they (or their signatures) have been removed. The masking or replacement of basaltic-to-intermediate glasses through alteration is supported by the appearance in the deconvolution solutions of amorphous phases (e.g., silica-rich glasses, opal) or phases with amorphous-like spectral signatures (e.g., clays, zeolites) that commonly form through aqueous alteration of mafic glasses. The glasses may still be important to local-scale thermal infrared studies given the basaltic nature of Mars and the variety of local-scale lithologies detected by various missions. The regional mineralogies derived from the NNLS deconvolution analysis divide into five statistically separable groups, which provide insight into regional trends in mineralogy. 相似文献
167.
168.
Benjamin M. Sleeter Terry L. Sohl Michelle A. Bouchard Ryan R. Reker Christopher E. Soulard William Acevedo Glenn E. Griffith Rachel R. Sleeter Roger F. Auch Kristi L. Sayler Stephen Prisley Zhiliang Zhu 《Global Environmental Change》2012,22(4):896-914
Global environmental change scenarios have typically provided projections of land use and land cover for a relatively small number of regions or using a relatively coarse resolution spatial grid, and for only a few major sectors. The coarseness of global projections, in both spatial and thematic dimensions, often limits their direct utility at scales useful for environmental management. This paper describes methods to downscale projections of land-use and land-cover change from the Intergovernmental Panel on Climate Change's Special Report on Emission Scenarios to ecological regions of the conterminous United States, using an integrated assessment model, land-use histories, and expert knowledge. Downscaled projections span a wide range of future potential conditions across sixteen land use/land cover sectors and 84 ecological regions, and are logically consistent with both historical measurements and SRES characteristics. Results appear to provide a credible solution for connecting regionalized projections of land use and land cover with existing downscaled climate scenarios, under a common set of scenario-based socioeconomic assumptions. 相似文献
169.
Anne D. Jungblut Michelle A. Allen Brendan P. Burns Brett A. Neilan 《Organic Geochemistry》2009,40(2):258-269
The lipid biomarker composition of microbial mat communities from three meltwater ponds from the McMurdo Ice Shelf, Antarctica, was investigated for the first time. Hydrocarbons, ether-linked components, fatty acids (FAs), wax esters, hopanols and sterols from Fresh, Orange and Salt Ponds were analysed. The dominance of cyanobacteria and the presence of bacterial sulfate reducers were confirmed using signature FAs in all three mats. Wax ester analysis suggested the presence of Chloroflexus spp. The dominance of short chain hydrocarbons, wax esters and FAs indicated that microorganisms are the major source of organic matter in these meltwater ponds. A variety of sterols were present in different relative abundances. The greatest diversity of sterols was in Salt Pond, followed by Fresh Pond, which was attributed to differences in the present eukaryotic diversity. Lipid profiles of the three communities were similar despite the presence of a salinity gradient. Analysis of lipid biomarkers allowed the creation of profiles for these unique Antarctic cryo-ecosystems. This will assist in the comparison of present and past microbial communities and in the monitoring of Antarctic biodiversity in response to global climate change and other environmental perturbations. 相似文献
170.
Effect of permafrost thaw on the dynamics of lakes recharged by ice‐jam floods: case study of Yukon Flats,Alaska
下载免费PDF全文
![点击此处可从《水文研究》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Large river floods are a key water source for many lakes in fluvial periglacial settings. Where permeable sediments occur, the distribution of permafrost may play an important role in the routing of floodwaters across a floodplain. This relationship is explored for lakes in the discontinuous permafrost of Yukon Flats, interior Alaska, using an analysis that integrates satellite‐derived gradients in water surface elevation, knowledge of hydrogeology, and hydrologic modelling. We observed gradients in water surface elevation between neighbouring lakes ranging from 0.001 to 0.004. These high gradients, despite a ubiquitous layer of continuous shallow gravel across the flats, are consistent with limited groundwater flow across lake basins resulting from the presence of permafrost. Permafrost impedes the propagation of floodwaters in the shallow subsurface and constrains transmission to ‘fill‐and‐spill’ over topographic depressions (surface sills), as we observed for the Twelvemile‐Buddy Lake pair following a May 2013 ice‐jam flood on the Yukon River. Model results indicate that permafrost table deepening of 1–11 m in gravel, depending on watershed geometry and subsurface properties, could shift important routing of floodwater to lakes from overland flow (fill‐and‐spill) to shallow groundwater flow (‘fill‐and‐seep’). Such a shift is possible in the next several hundred years of ground surface warming and may bring about more synchronous water level changes between neighbouring lakes following large flood events. This relationship offers a potentially useful tool, well suited to remote sensing, for identifying long‐term changes in shallow groundwater flow resulting from thawing of permafrost. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献