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651.
Jennifer Kung Baosheng Li Yanbin Wang Robert C. Liebermann 《Physics of the Earth and Planetary Interiors》2004,147(1):27-44
Using acoustic measurement interfaced with a large volume multi-anvil apparatus in conjunction with in situ X-radiation techniques, we are able to measure the density and elastic wave velocities (VP and VS) for both ortho- and high-pressure clino-MgSiO3 polymorphs in the same experimental run. The elastic bulk and shear moduli of the unquenchable high-pressure clinoenstatite phase were measured within its stability field for the first time. The measured density contrast associated with the phase transition OEN → HP-CEN is 2.6-2.9% in the pressure of 7-9 GPa, and the corresponding velocity jumps are 3-4% for P waves and 5-6% for S waves. The elastic moduli of the HP-CEN phase are KS=156.7(8) GPa, G = 98.5(4) GPa and their pressure derivatives are KS′=5.5(3) and G′ = 1.5(1) at a pressure of 6.5 GPa, room temperature. In addition, we observed anomalous elastic behavior in orthoenstatite at pressure above 9 GPa at room temperature. Both elastic wave velocities exhibited softening between 9 and 13-14 GPa, which we suggest is associated with a transition to a metastable phase intermediate between OEN and HP-CEN. 相似文献
652.
Dennis D. Kerkman David Stea Karen Norris Jennifer L. Rice 《The Professional geographer》2004,56(2):258-269
Three principal components were found to underlie Texas university students' experiences with and attitudes toward Canada, the United States, and Mexico: diversity orientation, Mexican experiences, and Canadian experiences. Diversity orientation included positive attitudes toward Hispanics, Canadians, minorities, interethnic friendships, and dating and was negatively correlated with natio‐centrism (e.g., believing U.S. citizens receive the world's best education). Diversity orientation and natio‐centrism were not related to experiences with Mexico or Canada. Students estimated the locations of Canadian cities too far north and Mexican cities too far south. Biased estimates for Mexican cities were negatively correlated with diversity orientation, not experience with Mexico. 相似文献
653.
Jennifer M. Mangan Jonathan T. Overpeck Robert S. Webb Carol Wessman Alexander F. H. Goetz 《Climatic change》2004,63(1-2):49-90
The Nebraska Sand Hills exist in a semi-arid climatic environment and the land surface is grassland growing on sandy soils. These soils have been periodically active throughout the Holocene, but are currently stabilized by the vegetation. However, a shift in climate could cause grassland death and eventual sand dune remobilization. Our studies used the CENTURY nutrient cycling and ecosystem model to investigate the impacts of drought, plant functional type, fire, grazing, and erosion on Nebraska Sand Hills vegetation and dune stability. Fire and grazing alone had little impact on the vegetation, but when combined with mild drought, biomass decreased. Overall biomass increased if one plant functional type was allowed to dominate the ecosystem. Addition of as little as 1 mm of erosion per year under current climate conditions decreases vegetation as much as a drought 20 percent drier than the worst of the 1930s drought years in Nebraska. 相似文献
654.
Jennifer Hyndman 《GeoJournal》2002,56(1):39-46
Transnational economic integration between Thailand and Burma is intimately linked to protection for Burmese refugees in Thailand.
In the case of Burmese nationals who seek safety in Thailand, their protection becomes more negotiable as economic integration
with Thailand proceeds. Since 1988, hundreds of thousands of Burmese citizens have fled beyond the borders of their state,
fearing both human rights abuses and successive offensives by a military junta intent on its own survival. Critical analysis
of the dynamic of human displacement and bi-national economic cooperation between the governments of Thailand Burma grounds
this study. The story is one of transnational trade across one border, where people's labour, homes, and passports are exchanged
– in an obscured fashion – for investment, natural resources, and economic cooperation. The Thai-Burmese border proves to
be a flexible concept that can be invoked to produce refugees or blurred to promote binational economic infrastructure and
trade. Despite economic booms and busts in Southeast Asia, economic integration in the region is on-going. At the same time,
Burma's government – the State Peace and Development Council – and its military force more and more citizens into neighbouring
countries. Their reception in Thailand, however, is increasingly chilly.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
655.
Jennifer L. Druhan James F. Hogan Christopher J. Eastoe Barry J. Hibbs William R. Hutchison 《Hydrogeology Journal》2008,16(2):281-296
Identification of hydrogeologic controls on groundwater flowpaths, recharge, and salinization is often critical to the management of limited arid groundwater resources. One approach to identifying these mechanisms is a combined analysis of hydrogeologic and hydrochemical data to develop a comprehensive conceptual model of a groundwater basin. To demonstrate this technique, water samples were collected from 33 discrete vertical zone test holes in the Hueco Bolson aquifer, located within the Trans-Pecos Texas region and the primary water resource for El Paso, Texas, USA and Juárez, Mexico. These samples were analyzed for a suite of geochemical tracers and the data evaluated in light of basin hydrogeology. On the basis of δ2H and δ18O data, two regional recharge sources were recognized, one originating from western mountain-fronts and one from through-flow of the adjacent Tularosa aquifer. Chloride concentrations were strongly correlated with lithologic formations and both Cl/Br and 36Cl ratios suggested the primary chloride source is halite dissolution within a specific lithologic unit. In contrast, sulfur isotopes indicated that most sulfate originates from Tularosa basin Permian gypsum sources. These results yielded a more comprehensive conceptual model of the basin, which suggested that chloride salinization of wells is the result of upconing of waters from the Fort Hancock formation. 相似文献
656.
An important ecological role ascribed to oysters is the transfer of materials from the water column to the benthos as they
feed on suspended particles (seston). This ecosystem service has been often touted as a major reason for many oyster restoration
efforts, but empirical characterization and quantification of seston removal rates in the field have been lacking. Changes
in chlorophyll a (chl a) concentrations in the water column were measured in May 2005 and June 2006 in South Carolina using in situ fluorometry and
laboratory analysis of pumped water samples taken upstream and downstream as water flowed over natural and constructed intertidal
oyster reefs. Both methods gave similar results overall, but with wide variability within individual reef datasets. In situ
fluorometer data logged at 10 to 30-s intervals for up to 1.3 h over eight different reefs (three natural and five constructed)
showed total removal (or uptake) expressed as % removal of chl a ranging from −9.8% to 27.9%, with a mean of 12.9%. Our data indicate that restored shellfish reefs should provide water-quality
improvements soon after construction, and the overall impact is probably determined by the size and density of the resident
filter feeder populations relative to water flow characteristics over the reef. The measured population-level chl a removal was converted to mean individual clearance rates to allow comparison with previous laboratory studies. Although direct
comparisons could not be made due to the small size of oysters on the study reefs (mean shell height, 36.1 mm), our calculated
rates (mean, 1.21 L h−1) were similar to published laboratory measured rates for oysters of this size. However, the wide variability in measured
removal by the oyster reefs suggests that individual oyster feeding rates in nature may be much more variable than in the
laboratory. The proliferation of ecosystem-level models that simulate the impacts of bivalves on water quality based only
on laboratory-feeding measurements underscores the importance of further research aimed at determining ecologically realistic
feeding rates for oysters in the field. Because in situ methods provide many replicate measurements quickly, they represent
a potentially powerful tool for quantifying the effects of oyster reefs, including all suspension-feeding taxa present, on
water quality. 相似文献
657.
Christel Prudhomme Andy Young Glenn Watts Tracey Haxton Sue Crooks Jennifer Williamson Helen Davies Simon Dadson Stuart Allen 《水文研究》2012,26(7):1115-1118
As climate change may modify the hydrological cycle significantly, understanding the impact on river flow is important because it affects long‐term water resources planning. Here, we describe a high‐resolution British assessment of changes in river flows in the 2050s under 11 different realisations of HadRM3. In winter, river flows may either increase or decrease, with a wide range of possible decreases in summer flow. These results should encourage adaptation that copes with a broad range of future hydrological conditions. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
658.
Jennifer L. Irish Ashley E. Frey Julie D. Rosati Francisco Olivera Lauren M. Dunkin James M. Kaihatu Celso M. Ferreira Billy L. Edge 《Ocean & Coastal Management》2010,53(10):645-657
Hurricane flooding is a leading natural threat to coastal communities. Recent evidence of sea level rise coupled with potential future global warming indicate that sea level rise will accelerate and hurricanes may intensify over the coming decades. In regions fronted by barrier islands, the protective capacity of these islands may diminish as they are degraded by rising sea level. Here we present a hydrodynamic and geospatial analysis of the relative role of barrier island degradation on potential future hurricane flooding. For the City of Corpus Christi, Texas, USA, hurricane flooding is projected to rise between 20% and 70% by the 2030s, resulting in an increase in property damages and impacted population. These findings indicate that adaptive management strategies should be developed and adopted for mitigating loss of natural barrier islands when these islands act as protective features for populated bayside communities. Finally, this study illustrates a method for applying models to forecast future storm protection benefits of barrier island restoration projects. 相似文献
659.
660.