全文获取类型
收费全文 | 198篇 |
免费 | 18篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 3篇 |
大气科学 | 26篇 |
地球物理 | 55篇 |
地质学 | 65篇 |
海洋学 | 9篇 |
天文学 | 20篇 |
自然地理 | 40篇 |
出版年
2023年 | 1篇 |
2022年 | 2篇 |
2021年 | 10篇 |
2020年 | 7篇 |
2019年 | 9篇 |
2018年 | 21篇 |
2017年 | 14篇 |
2016年 | 17篇 |
2015年 | 12篇 |
2014年 | 7篇 |
2013年 | 24篇 |
2012年 | 11篇 |
2011年 | 11篇 |
2010年 | 14篇 |
2009年 | 8篇 |
2008年 | 6篇 |
2007年 | 12篇 |
2006年 | 10篇 |
2005年 | 2篇 |
2004年 | 6篇 |
2003年 | 2篇 |
2002年 | 3篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1983年 | 1篇 |
1980年 | 2篇 |
1945年 | 1篇 |
排序方式: 共有218条查询结果,搜索用时 234 毫秒
1.
Jonathan F. Stebbins Emily V. Dubinsky Koji Kanehashi Kimberly E. Kelsey 《Geochimica et cosmochimica acta》2008,72(3):910-925
Configurational changes with temperature are important for the thermodynamic and transport properties of most aluminosilicate melts, but in general are not well understood. Here, we present high-resolution 27Al and 17O NMR data on several calcium aluminosilicate glasses prepared with varying quench rates and thus with fictive temperatures that span ranges up to about 200 K. In all compositions the content of five-coordinated aluminum increases with fictive temperature, in agreement with recent high temperature NMR data on melts. In a glass of CaAl2Si2O8 (“anorthite”) composition, the content of non-bridging oxygens also increases with temperature; however this effect was not observed in a sample with a much higher CaO/Al2O3 ratio. We present a consistent notation for reactions among structural species in these systems that clarify why in some cases, high-coordinated network cations may appear on the same side of the reaction, while in others they occur on the opposite sides: the key difference is in accounting for all coordination changes for oxygens. Mixing of non-bridging oxygens and of high-coordinated aluminum make significant contributions to the overall configurational entropy and heat capacity of the melts, as does the mixing of various bridging oxygens and of tetrahedral network cations. Other, less well known, types of increase in disorder with temperature may be important as well. 相似文献
2.
3.
汶川地震断裂作用研究新认识 总被引:2,自引:0,他引:2
王焕 李海兵 司家亮 孙知明 付小方 刘栋梁 裴军令 李成龙 张佳佳 宋圣荣 郭力伟 MORI James 薛莲 BRODSKY E. Emily 云锟 龚正 《地球学报》2015,36(3):257-269
2008年汶川地震后,人们不得不思考问题是:大地震是如何发生的?下一次大地震什么时候发生?也就是涉及地质学家和地球物理学家一直未解决的科学问题:断层是如何破裂的?震后断裂是如何愈合的?我们试图通过对汶川地震断裂带结构、断裂摩擦行为和断裂愈合过程的研究来回答这些问题。本文将介绍通过对地表露头和汶川地震断裂科学钻探一号孔(WFSD)岩心中汶川地震主滑移带的详细研究,以及钻孔中长期温度监测来分析有关汶川地震断裂动态弱化和摩擦行为,并结合钻孔中长期水文监测计算所得断裂带渗透率变化,分析震后断裂愈合过程,进而探讨和认识汶川地震断裂作用所涉及的上述问题。经过详细研究,确定了汶川地震断裂带(映秀—北川断裂带)宽105~240 m、具有五个不同断裂岩组合的内部结构,是一条经常发生大地震、具多种弱化机制的断裂带;发现了汶川地震不仅具有同震石墨化作用,而且测量到目前世界上最低的动态摩擦系数(≤0.02),同时首次记录到大地震后断裂快速愈合信息。这些研究结果不仅直接回答了一直困扰在地震地质和地震物理学领域几十年的关键问题,而且对完善地震断裂理论和认识汶川地震机制具有极其重要的意义,为防震减灾提供了理论依据。 相似文献
4.
大地震发生后立即在断层带上进行钻探可以帮助我们获取更多的地震信息,尤其是可获得决定断层动态破裂的摩擦水平和强度,观测断层的愈合过程及可能触发余震的应力变化,并可获取控制破裂过程的重要的物理和化学属性。在2008年11月由国际大陆科学钻探项目(ICDP)和南加州地震中心(SCEC)联合在日本东京举办的为期3天的“震后快速钻探:历史、现状与未来”研讨会上, 相似文献
5.
Joseph M. Delesantro Jonathan M. Duncan Diego Riveros-Iregui Joanna R. Blaszczak Emily S. Bernhardt Dean L. Urban Lawrence E. Band 《水文研究》2021,35(9):e14339
Current land-use classifications used to assess urbanization effects on stream water quality date back to the 1980s when limited information was available to characterize watershed attributes that mediate non-point source pollution. With high resolution remote sensing and widely used GIS tools, there has been a vast increase in the availability and precision of geospatial data of built environments. In this study, we leverage geospatial data to expand the characterization of developed landscapes and create a typology that allows us to better understand the impact of complex developed landscapes across the rural to urban gradient. We assess the ability of the developed landscape typology to reveal patterns in stream water chemistry previously undetected by traditional land-cover based classification. We examine the distribution of land-cover, infrastructure, topography and geology across 3876 National Hydrography Dataset Plus catchments in the Piedmont region of North Carolina, USA. From this dataset, we generate metrics to evaluate the abundance, density and position of landscape features relative to streams, catchment outlets and topographic wetness metrics. While impervious surfaces are a key distinguishing feature of the urban landscape, sanitary infrastructure, population density and geology are better predictors of baseflow stream water chemistry. Unsupervised clustering was used to generate a distinct developed landscape typology based on the expanded, high-resolution landscape feature information. Using stream chemistry data from 37 developed headwater catchments, we compared the baseflow water chemistry grouped by traditional land-cover based classes of urbanization (rural, low, medium and high density) to our composition and structure-based classification (a nine-class typology). The typology based on 22 metrics of developed landscape composition and structure explained over 50% of the variation in NO3−-N, TDN, DOC, Cl−, and Br− concentration, while the ISC-based classification only significantly explained 23% of the variation in TDN. These results demonstrate the importance of infrastructure, population and geology in defining developed landscapes and improving discrete classes for water management. 相似文献
6.
AbstractNatural resource challenges often span administrative jurisdictions and include actors and processes operating at different spatial and political scales. We applied concepts of new environmental governance to analyze Oregon’s approach to greater sage-grouse conservation. Through one in-depth case study in Lake County, we traced features of new environmental governance (cross-scale interactions, decentralization, and capacities of actors) through different governance levels. Interviews and qualitative analysis revealed that decentralization of administrative functions facilitated cross-scale interactions and relied on intermediaries, gap-filling, and perceptions of legitimacy at lower levels. State and agency guidelines steered the effort and were accompanied by financial and technical resources from multiple arenas, which increased local capacity. This study adds to the understandings of environmental governance for implementing multi-actor, multi-level conservation arrangements in resource-dependent communities. Further exploration of connections between higher levels and local contexts will reveal important, new ways to link policies with on-the-ground outcomes. 相似文献
7.
Emily Cloyd Susanne C. Moser Edward Maibach Julie Maldonado Tinqiao Chen 《Climatic change》2016,136(1):39-55
This paper examines the dynamics of energy investments and clean energy Research and Development (R&D) using a scenario-based modeling approach. Starting from the global scenarios proposed in the RoSE model ensemble experiment, we analyze the dynamics of investments under different assumptions regarding economic and population growth as well as availability of fossil fuel resources, in the absence of a climate policy. Our analysis indicates that economic growth and the speed of income convergence across countries matters for improvements in energy efficiency, both via dedicated R&D investments but mostly through capital-energy substitution. In contrast, fossil fuel prices, by changing the relative competitiveness of energy sources, create an economic opportunity for radical innovation in the energy sector. Indeed, our results suggest that fossil fuel availability is the key driver of investments in low carbon energy innovation. However, this innovation, by itself, is not sufficient to induce emission reductions compatible with climate stabilization objectives. 相似文献
8.
9.
The particulate organic matter (POM) in hydrodynamically variable habitats such as the lower reaches of estuaries can change in its content and quality on very short time scales (example, hourly), and these changes can potentially influence higher-level consumers in river-estuary-marine systems. Estuarine water samples were collected hourly for 12 h downstream in a small river to evaluate the fatty acid composition of POM over a tidal cycle. Fatty acid constituents of POM collected during the flood tide were dominated by the saturated, higher plant and bacterial fatty acids, whereas unsaturated, polyunsaturated, essential, and diatom-associated fatty acids dominated the POM collected during the ebb tide. Elevated algal biomass (as indicated by high chlorophyll a concentrations), diatom, and freshness indices in the POM indicated enhanced fresh autochthonous-origin materials that dominated the mixed organic pool during the ebb tide compared to more degraded detritus during the flood tide. Tidal retention of organic matter and algal primary production were the most influential factors that differentiated the fatty acid composition of estuarine POM over the short time scale. The results of this study have important implications on the quality of POM at the time of sampling, especially in estuaries where mixed organic pools have multiple inputs and are strongly influenced by tidal cycles. 相似文献
10.
Rockfall hazards increase the risk of train derailment along railway corridors in western Canada. In this study, repeated terrestrial laser scanning (TLS) datasets were collected every 2–3 months at three different sites along the Thompson and Fraser River corridors in British Columbia, referred to as the Goldpan, White Canyon, and Mile 109 sites. A total of 207 rockfall events occurring across all three sites between November 11, 2014 and October 18, 2016 were recorded in a database. For each of these rockfalls, pre-failure deformation was measured using a method of three-dimensional roto-translation block tracking. Each rockfall was classified by its deformation behaviour and further categorised based on failure mechanism, volume, lithology, and the roughness condition of the failure plane. Results reveal that detectable levels of deformation were measured in 33% of the total number of rockfall events using the present methods. Rotation deformation was most commonly observed in toppling failures with relatively steep joint orientations. Conversely, planar sliding blocks generally exhibited the least measurable deformation, with the majority not showing any precursory translation or rotation. It is postulated that overhanging rockfall configurations may suppress the expression of deformation in rockfall source blocks, though additional research is required to confirm this. 相似文献