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41.
Sea ice in the Barents Sea: seasonal to interannual variability and climate feedbacks in a global coupled model 总被引:1,自引:0,他引:1
Torben Koenigk Uwe Mikolajewicz Johann H. Jungclaus Alexandra Kroll 《Climate Dynamics》2009,32(7-8):1119-1138
Sea ice variability in the Barents Sea and its impact on climate are analyzed using a 465-year control integration of a global coupled atmosphere–ocean–sea ice model. Sensitivity simulations are performed to investigate the response to an isolated sea ice anomaly in the Barents Sea. The interannual variability of sea ice volume in the Barents Sea is mainly determined by variations in sea ice import into Barents Sea from the Central Arctic. This import is primarily driven by the local wind field. Horizontal oceanic heat transport into the Barents Sea is of minor importance for interannual sea ice variations but is important on longer time scales. Events with strong positive sea ice anomalies in the Barents Sea are due to accumulation of sea ice by enhanced sea ice imports and related NAO-like pressure conditions in the years before the event. Sea ice volume and concentration stay above normal in the Barents Sea for about 2 years after an event. This strongly increases the albedo and reduces the ocean heat release to the atmosphere. Consequently, air temperature is much colder than usual in the Barents Sea and surrounding areas. Precipitation is decreased and sea level pressure in the Barents Sea is anomalously high. The large-scale atmospheric response is limited with the main impact being a reduced pressure over Scandinavia in the year after a large ice volume occurs in the Barents Sea. Furthermore, high sea ice volume in the Barents Sea leads to increased sea ice melting and hence reduced surface salinity. Generally, the climate response is smallest in summer and largest in winter and spring. 相似文献
42.
Xavier D. Quintana Matías Arim Anna Badosa José María Blanco Dani Boix Sandra Brucet Jordi Compte Juan J. Egozcue Elvira de Eyto Ursula Gaedke Stéphanie Gascón Luis Gil de Solá Kenneth Irvine Erik Jeppesen Torben L. Lauridsen Rocío López-Flores Thomas Mehner Susana Romo Martin Søndergaard 《Aquatic Sciences - Research Across Boundaries》2015,77(1):45-57
43.
Future vegetation changes in thawing subarctic mires and implications for greenhouse gas exchange—a regional assessment 总被引:1,自引:1,他引:0
Julia Bosi? Margareta Johansson Terry V. Callaghan Bernt Johansen Torben R. Christensen 《Climatic change》2012,115(2):379-398
One of the major concerns regarding climate change in high latitudes is the potential feedback from greenhouse gases (GHG) being released from thawing peat soils. In this paper we show how vegetational patterns and associated GHG fluxes in subarctic palsa (peat mounds with a permanently frozen core) mires can be linked to climate, based on field observations from fifteen palsa sites distributed in northern Fennoscandia. Fine resolution (100?m) land cover data are combined with projections of future climate for the 21st century in order to model the potential future distribution of palsa vegetation in northern Fennoscandia. Site scale climate-vegetational relationships for two vegetation types are described by a climate suitability index computed from the field observations. Our results indicate drastic changes in the palsa vegetational patterns over the coming decades with a 97?% reduction in dry hummock areas by 2041?C2060 compared to the 1961?C1990 areal coverage. The impact of these changes on the carbon balance is a decrease in the efflux of CO2 from 130 kilotonnes C y?1 to a net uptake of 11 kilotonnes C y?1 and a threefold increase in the efflux of CH4 from 6 to 18 kilotonnes C y?1 over the same period and over the 5,520?km2 area of palsa mires. The combined effect is equivalent to a slight decrease in CO2-C emissions, from 182 to 152 kilotonnes C y?1. Main uncertainties involve the ability of the vegetation community to adapt to new conditions, and long-term changes in hydrology due to absence of ice and frost heaving. 相似文献
44.
Torben Koenigk Christof K?nig Beatty Mihaela Caian Ralf D?scher Klaus Wyser 《Climate Dynamics》2012,38(11-12):2389-2408
Decadal prediction is one focus of the upcoming 5th IPCC Assessment report. To be able to interpret the results and to further improve the decadal predictions it is important to investigate the potential predictability in the participating climate models. This study analyzes the upper limit of climate predictability on decadal time scales and its dependency on sea ice albedo parameterization by performing two perfect ensemble experiments with the global coupled climate model EC-Earth. In the first experiment, the standard albedo formulation of EC-Earth is used, in the second experiment sea ice albedo is reduced. The potential prognostic predictability is analyzed for a set of oceanic and atmospheric parameters. The decadal predictability of the atmospheric circulation is small. The highest potential predictability was found in air temperature at 2?m height over the northern North Atlantic and the southern South Atlantic. Over land, only a few areas are significantly predictable. The predictability for continental size averages of air temperature is relatively good in all northern hemisphere regions. Sea ice thickness is highly predictable along the ice edges in the North Atlantic Arctic Sector. The meridional overturning circulation is highly predictable in both experiments and governs most of the decadal climate predictability in the northern hemisphere. The experiments using reduced sea ice albedo show some important differences like a generally higher predictability of atmospheric variables in the Arctic or higher predictability of air temperature in Europe. Furthermore, decadal variations are substantially smaller in the simulations with reduced ice albedo, which can be explained by reduced sea ice thickness in these simulations. 相似文献
45.
Torben C. Rick Jon M. Erlandson René L. Vellanoweth Paul W. Collins Thomas W. Stafford Jr. 《Quaternary Research》2009,71(2):93-146
The island fox (Urocyon littoralis) is one of few reportedly endemic terrestrial mammals on California's Channel Islands. Questions remain about how and when foxes first colonized the islands, with researchers speculating on a natural, human-assisted, or combined dispersal during the late Pleistocene and/or Holocene. A natural dispersal of foxes to the northern Channel Islands has been supported by reports of a few fox bones from late Pleistocene paleontological localities. Direct AMS 14C dating of these “fossil” fox bones produced dates ranging from ∼ 6400 to 200 cal yr BP, however, postdating human colonization of the islands by several millennia. Although one of these specimens is the earliest securely dated fox from the islands, these new data support the hypothesis that Native Americans introduced foxes to all the Channel Islands in the early to middle Holocene. However, a natural dispersal for the original island colonization cannot be ruled out until further paleontological, archaeological, and genetic studies (especially aDNA [ancient DNA]) are conducted. 相似文献
46.
A first detailed look at the Greenland lithosphere and upper mantle, using Rayleigh wave tomography 总被引:2,自引:1,他引:2
47.
Torben C. Rick Gregory A. Henkes Darrin L. Lowery Steven M. Colman Brendan J. Culleton 《Quaternary Research》2012,77(1):205-210
Radiocarbon dates from known age, pre-bomb eastern oyster (Crassostrea virginica) shells provide local marine reservoir corrections (?R) for Chesapeake Bay and the Middle Atlantic coastal area of eastern North America. These data suggest subregional variability in ?R, ranging from 148 ± 46 14C yr on the Potomac River to ? 109 ± 38 14C yr at Swan Point, Maryland. The ?R weighted mean for the Chesapeake's Western Shore (129 ± 22 14C yr) is substantially higher than the Eastern Shore (? 88 ± 23 14C yr), with outer Atlantic Coast samples falling between these values (106 ± 46 and 2 ± 46 14C yr). These differences may result from a combination of factors, including 14C-depleted freshwater that enters the bay from some if its drainages, 14C-depleted seawater that enters the bay at its mouth, and/or biological carbon recycling. We advocate using different subregional ?R corrections when calibrating 14C dates on aquatic specimens from the Chesapeake Bay and coastal Middle Atlantic region of North America. 相似文献
48.
49.
Torben Birch-Thomsen Søren P. Kristensen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):23-37
Geografisk Tidsskrift, Danish Journal of Geography 105(2):23–37, 2005 As a reaction to the 'top-down 'approach to rural development during the 1970's and 1980's, and in line with the increased focus on ‘putting farmers first’ (bottom-up) through local participation, new and integrated approaches to natural resource management (NRM) have been launched to generate sustainable development. This paradigmatic change has greatly influenced land use planning. Some of the implications involved in this change are discussed in this paper and based on empirical data from Tanzania and Botswana. In this paper we will discuss three critical issues related to land use planning for sustainable NRM: the complexity of livelihood strategies at the local level, the role of different stakeholder interests and the importance of spatial scale considerations. The discussion emphasizes the importance of understanding that the different and often erratic resource endowment of the rural households influences the strategies these households follow in order to meet their overall needs, rather than ‘simply’ maximizing agricultural yields. Furthermore, the importance of spatial scale, in relation to both different stakeholder interests and their needs will be discussed. The paper highlights the need to take community heterogeneity into consideration in land use planning if sustainable NRM is to be achieved in the future. 相似文献
50.
Long-Term Profiles of Wind and Weibull Distribution Parameters up to 600 m in a Rural Coastal and an Inland Suburban Area 总被引:1,自引:1,他引:0
Sven-Erik Gryning Ekaterina Batchvarova Rogier Floors Alfredo Peña Burghard Brümmer Andrea N. Hahmann Torben Mikkelsen 《Boundary-Layer Meteorology》2014,150(2):167-184
An investigation of the long-term variability of wind profiles for wind energy applications is presented. The observations consists of wind measurements obtained from a ground-based wind lidar at heights between 100 and 600 m, in combination with measurements from tall meteorological towers at a flat rural coastal site in western Denmark and at an inland suburban area near Hamburg in Germany. Simulations with the weather research and forecasting numerical model were carried out in both forecast and analysis configurations. The scatter between measured and modelled wind speeds expressed by the root-mean-square error was about 10 % lower for the analysis compared to the forecast simulations. At the rural coastal site, the observed mean wind speeds above 60 m were underestimated by both the analysis and forecast model runs. For the inland suburban area, the mean wind speed is overestimated by both types of the simulations below 500 m. When studying the wind-speed variability with the Weibull distribution, the shape parameter was always underestimated by the forecast compared to both analysis simulations and measurements. At the rural coastal site although the measured and modelled Weibull distributions are different their variances are nearly the same. It is suggested to use the shape parameter for climatological mesoscale model evaluation. Based on the new measurements, a parametrization of the shape parameter for practical applications is suggested. 相似文献