全文获取类型
收费全文 | 276篇 |
免费 | 14篇 |
国内免费 | 8篇 |
专业分类
测绘学 | 5篇 |
大气科学 | 29篇 |
地球物理 | 100篇 |
地质学 | 94篇 |
海洋学 | 23篇 |
天文学 | 22篇 |
综合类 | 2篇 |
自然地理 | 23篇 |
出版年
2023年 | 2篇 |
2021年 | 3篇 |
2020年 | 5篇 |
2019年 | 3篇 |
2018年 | 12篇 |
2017年 | 8篇 |
2016年 | 10篇 |
2015年 | 10篇 |
2014年 | 11篇 |
2013年 | 31篇 |
2012年 | 16篇 |
2011年 | 17篇 |
2010年 | 18篇 |
2009年 | 11篇 |
2008年 | 12篇 |
2007年 | 8篇 |
2006年 | 17篇 |
2005年 | 14篇 |
2004年 | 13篇 |
2003年 | 11篇 |
2002年 | 8篇 |
2001年 | 7篇 |
2000年 | 9篇 |
1999年 | 4篇 |
1998年 | 8篇 |
1997年 | 3篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 2篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1982年 | 2篇 |
1981年 | 3篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有298条查询结果,搜索用时 31 毫秒
291.
ABSTRACTA popular rural development strategy in recent years has been through the adoption of what has been widely called a ‘value chain approach’, where improved linkages between small producers in underdeveloped rural communities and ‘lead firms’ constitute the foundations for development interventions. Whilst the global value-chain framework can deliver insights into the broad structural processes shaping livelihood possibilities, the adoption of value chains as a development strategy tends to disregard the complexity of smallholder livelihoods that shape poverty alleviation pathways in different contexts. The relationships between global value chains, development interventions, and rural livelihoods are explored in this article through a case study of smallholder coffee farming in the Toraja region of Indonesia. In this case, value-chain interventions in the coffee sector are unlikely to significantly contribute to improved rural welfare due to the diversified reality of local livelihoods, the nuances of how coffee production is embedded within Torajan culture and economy, and excellent prevailing market opportunities. The livelihood framework, therefore, provides an important corrective for the sometimes excessive optimism presented by advocates of a value-chain approach to rural development. 相似文献
292.
Sandstone‐hosted intrusions are found in a wide variety of environments, but remain poorly understood compared with their mudstone‐hosted counterparts. In particular, they remain largely unrecognized in the subsurface, in part because they are problematic to image in seismic data. This study reports on the facies and fluid flow associated with a 20 000 km3 sandstone intrusion province in Utah, USA. Forming a small portion of this intrusion province, the intrusions cropping out in Kodachrome Basin State Park display a very wide array of facies and morphologies, factors which would make their identification in core a significant challenge. Remobilized sediment is shown to have been injected at least 200 m vertically from its source, with flow prolonged enough to concentrate heavy minerals in placer‐style deposits at the pipe margins. Evidence for lateral pipe migration and for associated broader fluidization regions is also presented. A new approach to estimating flow parameters in injectites is implemented herein, and indicates that previous work has overestimated velocities and flow Reynolds numbers by up to two orders of magnitude. Flow modelling suggests turbulent flow in the pipes that is consistent with field observations of erosive margins and chaotic internal structures. Post‐emplacement, these pipes remained as long‐term fluid conduits, as revealed by their diagenetic history, focussing and facilitating flow of extraformational fluids, despite the relatively high porosity and permeability of the aeolian host strata. 相似文献
293.
Sharyn M. Hickey Stuart R. Phinn Nik J. Callow Kimberly P. Van Niel Jeff E. Hansen Carlos M. Duarte 《Estuaries and Coasts》2017,40(5):1215-1226
Ecological (poleward) regime shifts are a predicted response to climate change and have been well documented in terrestrial and more recently ocean species. Coastal zones are amongst the most susceptible ecosystems to the impacts of climate change, yet studies particularly focused on mangroves are lacking. Recent studies have highlighted the critical ecosystem services mangroves provide, yet there is a lack of data on temporal global population response. This study tests the notion that mangroves are migrating poleward at their biogeographical limits across the globe in line with climate change. A coupled systematic approach utilising literature and land surface and air temperature data was used to determine and validate the global poleward extent of the mangrove population. Our findings indicate that whilst temperature (land and air) have both increased across the analysed time periods, the data we located showed that mangroves were not consistently extending their latitudinal range across the globe. Mangroves, unlike other marine and terrestrial taxa, do not appear to be experiencing a poleward range expansion despite warming occurring at the present distributional limits. Understanding failure for mangroves to realise the global expansion facilitated by climate warming may require a focus on local constraints, including local anthropogenic pressures and impacts, oceanographic, hydrological, and topographical conditions. 相似文献
294.
High-resolution digital elevation models are crucial to the investigation of natural disasters, and a variety of methods based on visualization and relief map compilations have been proposed. In this study, the sky view factor (SVF) is applied to slope maps and a digital elevation model (DEM) of the Oso landslide, a deadly landslide that occurred in Washington State on March 22, 2014, to demonstrate the effectiveness of SVF-enhanced relief maps in mapping and evaluating large-scale or deep-seated landslide hazards. A procedure for combining the SVF-enhanced DEM with slope and elevation maps is also presented. Then the maps are used to extract the landslide-prone areas and perform a reactivation analysis of the post-Oso landslide using an analytic hierarchy process (AHP). By using the SVF-enhanced DEM to perform the AHP assessment on multi-period images, we accurately evaluate hazard of the landslide for both pre and post-2014 conditions. Finally, different visualization maps, limitation and recommend parameters for generating SVF relief map are presented in the paper. 相似文献
295.
L. Mahrt Dean Vickers Jim Edson James M. Wilczak Jeff Hare Jørgen Højstrup 《Boundary-Layer Meteorology》2001,100(1):47-61
The adjustment of the boundary layer immediately downstream froma coastline is examined based on two levels of eddy correlation data collected on a mast at the shore and six levels of eddy correlation data and profiles of mean variables collected from a mast 2 km offshore during the Risø Air-Sea Experiment. The characteristics of offshore flow are studied in terms of case studies and inter-variable relationships for the entire one-month data set. A turbulent kinetic energy budget is constructed for each case study.The buoyancy generation of turbulence is small compared to shear generation and dissipation. However, weakly stable and weakly unstable cases exhibit completely different vertical structure. With flow of warm air from land over cooler water, modest buoyancy destruction of turbulence and reduced shear generation of turbulence over the less rough sea surface cause the turbulence to rapidly weaken downstream from the coast. The reduction of downward mixing of momentum by the stratification leads to smaller roughness lengths compared to the unstable case. Shear generation at higher levels and advection of stronger turbulence from land often lead to an increase of stress and turbulence energy with height and downward transport of turbulence energy toward the surface.With flow of cool air over a warmer sea surface, a convective internal boundary layer develops downstream from the coast. An overlying relatively thick layer of downward buoyancy flux (virtual temperature flux) is sometimes maintained by shear generation in the accelerating offshore flow. 相似文献
296.
Stewart Cohen Denise Neilsen Scott Smith Tina Neale Bill Taylor Mark Barton Wendy Merritt Younes Alila Philippa Shepherd Roger Mcneill James Tansey Jeff Carmichael Stacy Langsdale 《Climatic change》2006,75(3):331-358
The research activity described in this report is a comprehensive regional assessment of the impacts of climate change on
water resources and options for adaptation in the Okanagan Basin. The ultimate goal of the project is to develop integrated
climate change and water resource scenarios to stimulate a multistakeholder discussion on the implications of climate change
for water management in the region.
The paper describes two main objectives: (a) providing a set of research products that will be of relevance to regional interests
in the Okanagan, and (b) establishing a methodology for participatory integrated assessment of regional climate change impacts
and adaptation that could be applied to climate-related concerns in Canada and other countries.
This collaborative study has relied on field research, computer-based models, and dialogue exercises to generate an assessment
of future implications, and to learn about regional views on the prospects for adaptation. Along the way, it has benefited
from strong partnerships with governments, researchers, local water practitioners, and user groups. Building on the scenario-based
study components, and a series of interviews and surveys undertaken for the water management and adaptation case study components,
a set of stakeholder dialogue sessions were organized which focused on identifying preferred adaptation options and processes
for their implementation. Rather than seeking consensus on the “best” option or process, regional interests were asked to
consider a range of available options as part of an adaptation portfolio that could address both supply side and demand side
aspects of water resources management in the Okanagan.
The Canadian Crown reserves the right to retain a non-exclusive, royalty free licence in and to any copyright. 相似文献
297.
David B. Madsen Li Jingzen Robert G. Elston Xu Cheng Robert L. Bettinger Geng Kan P. Jeff Brantingham Zhong Kan 《Geoarchaeology》1998,13(8):847-869
The use of latest Pleistocene-Holocene paleosols in defining Chinese climatic sequences is plagued by poor chronological controls caused primarily by the use of radiocarbon dates derived from bulk soil carbon. Dating of a post-glacial aeolian/paleosol sequence in the Pigeon Mountain basin of north-central China, using culturally deposited charcoal, support a wide array of other data suggesting the Younger Dryas was a period of cooler dryer conditions marked by wide-spread aeolian deposition. Periods of soil formation and higher lake levels bracket this climatic event. Climatic variability immediately before, during and immediately after the Younger Dryas interval is associated with rapid technological elaboration and innovation in the production and use of chipped stone tools, and perhaps, ground stone. © 1998 John Wiley & Sons, Inc. 相似文献
298.
The Aegean island of Thera (Santorini) was covered by tephra from its cataclysmic Late Bronze Age (ca. 3600 yr B.P.) eruption. Vertical exposures of the eruptive sequence show secondary, nonvolcanic, circular (in cross section) features composed of stratified sediment. Many are inaccessible from the floors of modern quarries and appear to be caves filled with younger sediment, but show no connection to the land surface. A filled cave was found in the wall of a modern gully outside the modern quarries, and a filled cave was found in a terrace scarp, well above the modern gully. Natural (and probably rapid) incision by gullies into the thick tephra deposit left many locations with lateral access to tephra. Inhabitants from post‐Minoan to recent times excavated tephra for materials and buildings, and caves were subsequently filled by sporadic (possibly seasonal) flood events that deposited sediment. These gullies may have provided access for modern tephra removal that isolated the filled caves high on the modern quarry walls. © 2003 Wiley Periodicals, Inc. 相似文献