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排序方式: 共有118条查询结果,搜索用时 828 毫秒
61.
500-year temperature reconstruction in the Mediterranean Basin by means of documentary data and instrumental observations 总被引:3,自引:1,他引:2
Dario Camuffo C. Bertolin M. Barriendos F. Dominguez-Castro C. Cocheo S. Enzi M. Sghedoni A. della Valle E. Garnier M.-J. Alcoforado E. Xoplaki J. Luterbacher N. Diodato M. Maugeri M. F. Nunes R. Rodriguez 《Climatic change》2010,101(1-2):169-199
The paper reports the main results of the EU project Millennium in the Mediterranean area over the last 500 years. It analyses a long series of temperature from Portugal, Spain, France, Italy and Greece. The series are obtained by combining indices from documentary sources from AD 1500 to the onset of regular instrumental observations. There is an ongoing discussion regarding the proper way of combining documentary and instrumental data and how to translate accurately the conventional indices from ??3 to +?3 into modern units, i.e. degree Celsius. This paper produces for the first time a number of early instrumental observations, in some cases (i.e. Italy and France) covering 350 years, including thereby the earliest regular observations after the invention of the thermometer. These Mediterranean data show that anomalous temperatures usually had only a locally limited effect, while only few extreme events had a widespread impact over the whole region, such as the summer of 2003. During the period from 1850 to the present day, the Mediterranean temperature anomaly was close to the Northern Hemisphere in spring and summer, while it was warmer in autumn and winter. Compared with the long-term instrumental records (i.e. 1655 onwards), the recent warming has not exceeded the natural past variability characterized by heating–cooling cycles with no significant long-term trends. 相似文献
62.
Fabien Gibert Irène Xuéref-Rémy Lilian Joly Martina Schmidt Juan Cuesta Kenneth J. Davis Michel Ramonet Pierre H. Flamant Bertrand Parvitte Virginie Zéninari 《Boundary-Layer Meteorology》2008,128(3):381-401
A network of remote and in-situ sensors was deployed in a Paris suburb in order to evaluate the mesoscale evolution of the
daily cycle of CO2 and related tracers in the atmospheric boundary layer (ABL) and its relation to ABL dynamics and nearby natural and anthropogenic
sources and sinks. A 2-μm heterodyne Doppler differential absorption lidar, which combines measurements of, (1) structure
of the atmosphere, (2) radial velocity, and (3) CO2 differential absorption was a particularly unique element of the observational array. We analyse the differences in the diurnal
cycle of CO, CO2, lidar reflectivity (a proxy for aerosol content) and H2O using the lidar, airborne measurements in the free troposphere and ground-based measurements made at two sites located few
kilometres apart. We demonstrate that vertical mixing dominates the early morning drawdown of CO and aerosol content trapped
in the former nocturnal layer but not the H2O and CO2 mixing ratio variations. Surface fluxes, vertical mixing and advection all contribute to the ABL CO2 mixing ratio decrease during the morning transition, with the relative importance depending on the rate and timing of ABL
rise. We also show evidence that when the ABL is stable, small-scale (0.1-km vertical and 1-km horizontal) gradients of CO2 and CO are large. The results illustrate the complexity of inferring surface fluxes of CO2 from atmospheric budgets in the stable boundary layer. 相似文献
63.
Most state-of-the art global coupled models simulate a weakening of the Atlantic meridional overturning circulation (MOC)
in climate change scenarios but the mechanisms leading to this weakening are still being debated. The third version of the
CNRM (Centre National de Recherches Météorologiques) global atmosphere-ocean-sea ice coupled model (CNRM-CM3) was used to
conduct climate change experiments for the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4).
The analysis of the A1B scenario experiment shows that global warming leads to a slowdown of North Atlantic deep ocean convection
and thermohaline circulation south of Iceland. This slowdown is triggered by a freshening of the Arctic Ocean and an increase
in freshwater outflow through Fram Strait. Sea ice melting in the Barents Sea induces a local amplification of the surface
warming, which enhances the cyclonic atmospheric circulation around Spitzberg. This anti-clockwise circulation forces an increase
in Fram Strait outflow and a simultaneous increase in ocean transport of warm waters toward the Barents Sea, favouring further
sea ice melting and surface warming in the Barents Sea. Additionally, the retreat of sea ice allows more deep water formation
north of Iceland and the thermohaline circulation strengthens there. The transport of warm and saline waters toward the Barents
Sea is further enhanced, which constitutes a second positive feedback. 相似文献
64.
A preindustrial climate experiment was conducted with the third version of the CNRM global atmosphere–ocean–sea ice coupled
model (CNRM-CM3) for the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC AR4). This experiment is
used to investigate the main physical processes involved in the variability of the North Atlantic ocean convection and the
induced variability of the Atlantic meridional overturning circulation (MOC). Three ocean convection sites are simulated,
in the Labrador, Irminger and Greenland–Iceland–Norwegian (GIN) Seas in agreement with observations. A mechanism linking the
variability of the Arctic sea ice cover and convection in the GIN Seas is highlighted. Contrary to previous suggested mechanisms,
in CNRM-CM3 the latter is not modulated by the variability of freshwater export through Fram Strait. Instead, the variability
of convection is mainly driven by the variability of the sea ice edge position in the Greenland Sea. In this area, the surface
freshwater balance is dominated by the freshwater input due to the melting of sea ice. The ice edge position is modulated
either by northwestward geostrophic current anomalies or by an intensification of northerly winds. In the model, stronger
than average northerly winds force simultaneous intense convective events in the Irminger and GIN Seas. Convection interacts
with the thermohaline circulation on timescales of 5–10 years, which translates into MOC anomalies propagating southward from
the convection sites. 相似文献
65.
Christophe Fontanier Takashi Toyofuku Eline Garnier Christophe Brandily Thibaut Eugene Bruno Deflandre 《Journal of Oceanography》2017,73(2):259-275
Oxygen and carbon isotopes (δ18O and δ13C) have been investigated in carbonate tests of deep-sea foraminifera living in the Mozambique Channel (eastern Africa) to understand how environmental constraints (e.g., organic matter, oxygenation) control the intra- and interspecific variability of isotopic signatures. 197 living individuals, including eight different species, from various microhabitats within the sediment were sorted from sediment samples gathered at two stations on the Malagasy upper slope. Results show that the δ18O values of foraminiferal taxa were not controlled by microhabitat pattern. They presented tremendous and intriguing intraspecific variability that is not explained by the classical ontogenetic effect. The δ13C values of infaunal foraminiferal taxa do not show a 1:1 relationship with the bottom water δ13C DIC and do not present a constant offset from it; instead, they appear to be mainly controlled by a microhabitat effect. The lower δ13C values of shallow, intermediate, and deep infaunal taxa at the deeper station compared to those seen at the shallower station reflect the enhanced exportation of sedimentary organic matter at the sediment–water interface, and its related mineralization within the upper sediments. The ?δ13C between shallow/very shallow infaunal species (i.e., Hoeglundina elegans, Uvigerina hispida) and intermediate/deep infaunal species (i.e., Melonis barleeanus, Globobulimina barbata) permits insight into (1) the exportation of organic matter to the seafloor and (2) the various degradation pathways for organic detritus in the benthic environments off NW Madagascar. 相似文献
66.
Giloy Nathalie Hamdi Yasser Bardet Lise Garnier Emmanuel Duluc Claire-Maire 《Natural Hazards》2019,98(3):869-893
Natural Hazards - As instrumental records often cover only short time periods, historical information is the main source of data in order to extend natural disaster catalogs. This study... 相似文献
67.
To simulate the behavior of radionuclides along a salinity gradient, in vitro sorption and desorption kinetics of Co, Mn, Cs, Fe, Ag, Zn and Cd were studied in Loire river water and the macrotidal Loire estuarine water over two different seasons. Partitioning between the dissolved phase and suspended solids were followed up over 100 h after adding radioactive tracers to freshly collected freshwater (sorption stage); this stage was followed by desorption in fresh and estuarine waters. A kinetic model describing the interactions between trace metals and particles under a salinity gradient was developed and calibrated. Among parameters and/or processes that control the fate and behavior of contaminated particles during their transfer in estuarine systems, this study shows that the speciation of trace metals is controlled by: (i) the chemical water composition: for all the elements except for Fe, desorption increased with salinity; however, the amplitude of such an effect strongly depended on the element and/or on the composition of the particulate phase (and consequently on the season); (ii) the possibility for a given element to form (or not) stable surface particle moieties such as oxides or inner-sphere complexes; (iii) the distribution of a given element among different types of sites characterised by different binding forces that can lead (or not) to re-adsorption processes after mixing of contaminated particles with uncontaminated water.Our model enabled the quantification of the contribution and the characteristic time of reactions that took place over short and long periods on the global partitioning between particulate and dissolved phases during sorption and desorption and to determine the extent to which these reactions were modified by the salinity. 相似文献
68.
The unique database of water quality measurements made in the Seine estuary over 45 years by the Service de la Navigation de la Seine at Rouen is used here to reconstruct the evolution of oxygen status in the estuary and the nutrient fluxes to the Seine Bight during the last half century. The Riverstrahler model is used to establish the link between these long-term trends in the functioning of the Seine system and the evolution of agricultural, domestic, and industrial activity in the watershed over this period taking into account natural and man-induced hydrological variations. Oxygenation of the fluvial sector below Paris has increased considerably owing to improved wastewater treatment, but a large part of the estuary remains completely anoxic during the spring and summer months. Nitrogen input to surface waters from urban sources has remained essentially constant while diffuse inputs from agricultural soils have increased 5-fold as a result of more intensive agricultural practices as well as the loss of retention capacity in riparian zones. Phosphorus inputs from domestic and industrial sources increased 3-fold from 1950 to 1980, but have decreased gradually in recent years. The generally high level of phosphorus contamination has favored strong algal development in all large tributaries of the Seine River upstream of paris since the 1960s. Silica inputs, originating mainly from the weathering of rocks, fluctuate widely depending on hydrology. In-stream retention of silica, linked to diatom blooms, has increased but remains limited. These changes have induced several shifts in the nutrient limitation conditions of the Seine Bight. 相似文献
69.
A chain of three nested models, based on the MARS 3D code, is used to simulate the North-western Mediterranean Sea circulation
with a finest grid of 1.2 km resolution and 30 vertical sigma levels. This modelling system allows to resolve the coastal
dynamics taking into account the influence of the general basin circulation. The aim of this study is to assess the ability
of the nested MARS-3D models to reproduce most of the circulation features observed in the North-western Mediterranean Basin
and in the Gulf of Lions. Comparisons of modelled sea surface temperature and salinity with MEDAR/MEDATLAS climatology and
NOAA/AVHRR satellite measurements show that the model accurately reproduces the large and coastal scale variability. Over
the Northern Basin, the seasonal changes of the cyclonic gyre extension are correctly simulated, even though in summer, the
modelled temperature of the surface layer remains in basin-average 1°C cooler than the satellite measured temperature. As
soon as the stratification erodes, modelled and observed temperatures become closer. Over the Gulf of Lions, realistic coastal
responses are obtained under different wind conditions. Upwellings are correctly located and their intensity and spatial extension
were here improved by the use of Aladin wind fields (10 km spatial resolution) and the introduction of a drag coefficient
fitted according to the stability of the planetary boundary layer. The dispersion of fresh Rhone water discharge and the mesoscale
circulation simulated by MARS-3D also agree with satellite measurements. 相似文献
70.
Michel Chouteau Stefka Krivochieva Ramiro Rodriguez Castillo Tomas Gonzalez Moran Virginie Jouanne 《Journal of Applied Geophysics》1994,31(1-4)
A tensor magnetotelluric test survey was carried out in the region of Santa Catarina, located in the Chalco sub-basin of the Mexico Basin. The objective was to define the stratification at depth with an emphasis on the geometry of the main aquifer of that region which is partially known from DC resistivity soundings and drilling. High-quality magnetotelluric soundings could be recorded in the immediate vicinity of large urban zones because the sub-surface is very conductive. Interpretation shows that the solid bedrock is located at a depth of at least 800 m to the south and 1300 m to the north; it could, however, be much deeper. Using complementary DC resistivity sounding and well-logging data, three main layers have been defined overlying the bedrock. These layers are, from surface to bottom, an unsaturated zone of sand, volcanic ash and clay about 10 m thick, followed by a very conductive (1.5 ohm·m) 200 m thick layer of sand and ash with intercalated clay, saturated with highly mineralized water, and finally a zone with resistivity increasing gradually to 60 ohm·m. The investigated deep aquifer constitutes most of this third layer. It consists of a sequence of sand, gravel, pyroclastites and mainly fractured basalts. MT resistivity soundings and magnetic transfer functions also indicate that a shallow resistive structure is dipping, from the northwest, into the lacustrine deposits of the basin. This geologic feature is likely to be highly permeable fractured basaltic flows, which provide a channel by which water contaminated by the Santa Catarina landfill may leak into the basin. 相似文献