全文获取类型
收费全文 | 123篇 |
免费 | 5篇 |
国内免费 | 1篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 22篇 |
地球物理 | 35篇 |
地质学 | 32篇 |
海洋学 | 15篇 |
天文学 | 22篇 |
自然地理 | 2篇 |
出版年
2021年 | 4篇 |
2020年 | 2篇 |
2018年 | 2篇 |
2017年 | 5篇 |
2016年 | 14篇 |
2015年 | 6篇 |
2014年 | 5篇 |
2013年 | 7篇 |
2012年 | 6篇 |
2011年 | 13篇 |
2010年 | 9篇 |
2009年 | 10篇 |
2008年 | 6篇 |
2007年 | 5篇 |
2006年 | 9篇 |
2005年 | 4篇 |
2004年 | 7篇 |
2003年 | 1篇 |
2002年 | 1篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1998年 | 3篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1993年 | 1篇 |
1985年 | 1篇 |
1982年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有129条查询结果,搜索用时 15 毫秒
71.
Sébastien Lefebvre Julio César Marín Leal Stanislas Dubois Francis Orvain Jean-Louis Blin Marie-Paule Bataillé Alain Ourry Robert Galois 《Estuarine, Coastal and Shelf Science》2009
The temporal dynamics of carbon and nitrogen isotope values of co-occurring suspension-feeders in two shellfish culture areas (Normandy, France) were investigated over two years to evaluate the inter-specific trophic partitioning and relative contributions of organic matter sources to benthic suspension-feeders' diet. Oysters (Crassostrea gigas), mussels (Mytilus edulis), cockles (Cerastoderma edule), slipper limpets (Crepidula fornicata), and sand-mason worms (Lanice conchilega) were sampled in an estuarine environment (Baie des Veys, east Cotentin, Normandy), while oysters, mussels, slipper limpets, and honeycomb worms (Sabellaria alveolata) were sampled in an open-marine environment (Lingreville-sur-mer, west Cotentin, Normandy). Whatever the sampling period, the bivalves, C. gigas and M. edulis, exhibited the lowest values of δ13C and δ15N compared with the other species. Feeding relationships among suspension-feeders in both C. gigas culture areas exhibited temporal variations due to the marine/estuarine influence and seasonal changes in food supply. In the open-marine ecosystem, the contribution of phytoplankton remained the most important for all species except S. alveolata, while in the estuarine ecosystem, microphytobenthos and/or macroalgae detritus contributed a larger extent to the organisms' diets. During phytoplankton bloom periods (e.g. May and July) suspension-feeders, except for S. alveolata, relied strongly on phytoplankton; however, the majority of suspension-feeders exhibited different opportunistic behaviour in winter when phytoplankton biomass might be a limiting factor. We hypothesized that differences in particle capture and selection by the suspension-feeders influenced their isotopic values. Feeding ecology of suspension-feeders partly explained why competition was limited and why ecosystems can often support unexpectedly large numbers of suspension-feeders. We also showed that understanding ecosystem characteristics of the organic matter sources is of primary importance to determine the extent to which members of the suspension-feeding guild potentially compete for food. 相似文献
72.
Sandrine D’Hoedt Benoît Noyelles Julien Dufey Anne Lemaître 《Celestial Mechanics and Dynamical Astronomy》2010,107(1-2):93-100
The resonant rotation of Mercury can be modelised by a kernel model on which we can add perturbations. Our kernel model is a two-degree of freedom one written in Hamiltonian formalism. For this kernel, we consider that Mercury is solid and rotates on a Keplerian orbit. By introducing the perturbations due to the other planets of the Solar System, it appears that, in a particular case, our slow degree of freedom may enter into a 1:1 resonance with the Great Inequality of Jupiter and Saturn. Actually, as the moments of inertia of Mercury are still poorly known, this phenomenon cannot be excluded. 相似文献
73.
Comparative study of methods for WHPA delineation 总被引:3,自引:0,他引:3
Paradis D Martel R Karanta G Lefebvre R Michaud Y Therrien R Nastev M 《Ground water》2007,45(2):158-167
Human activities, whether agricultural, industrial, commercial, or domestic, can contribute to ground water quality deterioration. In order to protect the ground water exploited by a production well, it is essential to develop a good knowledge of the flow system and to adequately delineate the area surrounding the well within which potential contamination sources should be managed. Many methods have been developed to delineate such a wellhead protection area (WHPA). The integration of more information on the geologic and hydrogeologic characteristics of the study area increases the precision of any given WHPA delineation method. From a practical point of view, the WHPA delineation methods allowing the simplest and least expensive integration of the available information should be favored. This paper presents a comparative study in which nine different WHPA delineation methods were applied to a well and a spring in an unconfined granular aquifer and to a well in a confined highly fractured rock aquifer. These methods range from simple approaches to complex computer models. Hydrogeological mapping and numerical modeling with MODFLOW-MODPATH were used as reference methods to respectively compare the delineation of the zone of contribution and the zone of travel obtained from the various WHPA methods. Although applied to simple ground water flow systems, these methods provided a relatively wide range of results. To allow a realistic delineation of the WHPA in aquifers of variable geometry, a WHPA delineation method should ensure a water balance and include observed or calculated regional flow characteristics. 相似文献
74.
Parasite species have been widely used as fish host migration tag or as indicators of local pollution. In this paper our approach is to consider the entire parasite community as a biological indicator of the fish environmental conditions. Seven fish species belonging to the Apogonidae, Apogon bandanensis, A. cookii, A. doderleini, A. norfolkensis, A. trimaculatus, Cheilodipterus quinquelineatus and Fowleria variegata, were sampled on six stations in two bays (Grand-Rade and Sainte-Marie) around Nouméa (New-Caledonia). The two bays are submitted to urban wastewater inputs alone or combined with additional industrial inputs which influences decrease from the inner part to the entrance of each bay. A total of 592 fish were dissected for macro parasite examination. Parasites were grouped according to their taxonomical rank and development stage for the analysis. We found an inconsistent effect of the confinement between the two bays, revealing that the parasite community is not the same in the two bays. Moreover, the encysted metacercariae found in the pericardic cavity were found to be significant indicators of the specific anthropogenically impacted environmental conditions prevailing in the inner parts of the two bays. Other parasite taxa were found to be significant indicators of specific environmental conditions in one or two stations among the six sampled. Results on parasite specificity and biological life cycle of the parasite taxa found in sampled Apogonid were further compared with environmental parameters. 相似文献
75.
Athena Coustenis Richard K. Achterberg Donald E. Jennings Daniel Gautier F. Michael Flasar Bruno Bézard Ronald C. Carlson Gordon L. Bjoraker Fred W. Taylor Thierry Fouchet Glenn S. Orton Sandrine Vinatier Mian M. Abbas 《Icarus》2007,189(1):35-62
We have analyzed data recorded by the Composite Infrared Spectrometer (CIRS) aboard the Cassini spacecraft during the Titan flybys T0-T10 (July 2004-January 2006). The spectra characterize various regions on Titan from 70° S to 70° N with a variety of emission angles. We study the molecular signatures observed in the mid-infrared CIRS detector arrays (FP3 and FP4, covering roughly the 600-1500 cm−1 spectral range with apodized resolutions of 2.54 or 0.53 cm−1). The composite spectrum shows several molecular signatures: hydrocarbons, nitriles and CO2. A firm detection of benzene (C6H6) is provided by CIRS at levels of about 3.5×10−9 around 70° N. We have used temperature profiles retrieved from the inversion of the emission observed in the methane ν4 band at 1304 cm−1 and a line-by-line radiative transfer code to infer the abundances of the trace constituents and some of their isotopes in Titan's stratosphere. No longitudinal variations were found for these gases. Little or no change is observed generally in their abundances from the south to the equator. On the other hand, meridional variations retrieved for these trace constituents from the equator to the North ranged from almost zero (no or very little meridional variations) for C2H2, C2H6, C3H8, C2H4 and CO2 to a significant enhancement at high northern (early winter) latitudes for HCN, HC3N, C4H2, C3H4 and C6H6. For the more important increases in the northern latitudes, the transition occurs roughly between 30 and 50 degrees north latitude, depending on the molecule. Note however that the very high-northern latitude results from tours TB-T10 bear large uncertainties due to few available data and problems with latitude smearing effects. The observed variations are consistent with some, but not all, of the predictions from dynamical-photochemical models. Constraints are set on the vertical distribution of C2H2, found to be compatible with 2-D equatorial predictions by global circulation models. The D/H ratio in the methane on Titan has been determined from the CH3D band at 1156 cm−1 and found to be . Implications of this deuterium enrichment, with respect to the protosolar abundance on the origin of Titan, are discussed. We compare our results with values retrieved by Voyager IRIS observations taken in 1980, as well as with more recent (1997) disk-averaged Infrared Space Observatory (ISO) results and with the latest Cassini-Huygens inferences from other instruments in an attempt to better comprehend the physical phenomena on Titan. 相似文献
76.
Vincent Cloutier René Lefebvre Martine M. Savard René Therrien 《Environmental Earth Sciences》2010,59(5):977-994
The objective of this study was to identify geochemical processes and Quaternary geological events responsible for the variations
in groundwater geochemistry observed in a sedimentary rock aquifer system, including brackish to saline groundwater. Inorganic
constituents and environmental isotopes were analyzed for 146 groundwater samples. Dissolution of carbonates dominates in
recharge areas, resulting in Ca-, Mg-HCO3 groundwater. Further along flow paths, under confined conditions, Ca2+–Na+ ion exchange causes groundwater evolution to Na-HCO3 type. Na-Cl groundwater is also found and it falls on a seawater mixing line. Using conservative tracers, Cl− and Br−, the original Champlain Sea water is shown to have been, in the region, a mixture of about 34% seawater and 66% freshwater,
a composition still retained by some groundwater. Na-Cl groundwater thus results from mixing with former Champlain Sea water
and also from solute diffusion from overlying marine clay. The system is thus found to be at different stages of desalinization,
from the original Champlain Sea water still present in hydraulically stagnant areas of the aquifer to fully flushed conditions
in parts, where more flow occurs, especially in recharge zones. The geochemical processes are integrated within the hydrogeological
context to produce a conceptual geochemical evolution model for groundwater of the aquifer system. 相似文献
77.
Hugues Goosse Wouter Lefebvre Anne de Montety Elisabeth Crespin Alejandro H. Orsi 《Climate Dynamics》2009,33(7-8):999-1016
Simulations performed with the climate model LOVECLIM, aided with a simple data assimilation technique that forces a close matching of simulated and observed surface temperature variations, are able to reasonably reproduce the observed changes in the lower atmosphere, sea ice and ocean during the second half of the twentieth century. Although the simulated ice area slightly increases over the period 1980–2000, in agreement with observations, it decreases by 0.5 × 106 km2 between early 1960s and early 1980s. No direct and reliable sea ice observations are available to firmly confirm this simulated decrease, but it is consistent with the data used to constrain model evolution as well as with additional independent data in both the atmosphere and the ocean. The simulated reduction of the ice area between the early 1960s and early 1980s is similar to the one simulated over that period as a response to the increase in greenhouse gas concentrations in the atmosphere while the increase in ice area over the last decades of the twentieth century is likely due to changes in atmospheric circulation. However, the exact contribution of external forcing and internal variability in the recent changes cannot be precisely estimated from our results. Our simulations also reproduce the observed oceanic subsurface warming north of the continental shelf of the Ross Sea and the salinity decrease on the Ross Sea continental shelf. Parts of those changes are likely related to the response of the system to the external forcing. Modifications in the wind pattern, influencing the ice production/melting rates, also play a role in the simulated surface salinity decrease. 相似文献
78.
Reference emission scenarios in the literature have been the target of criticisms that suggest they convey too optimistic views on spontaneous energy-GDP decoupling of emerging countries economies. This article focuses on the case of India. It explores the role of current suboptimalities of the Indian power sector (structural under-investment in the sector leading to capacity shortage, power cuts and low efficiency) on future energy-GDP decoupling. To do so, it uses a hybrid general equilibrium framework, in which these suboptimalities are explicitly introduced. The results highlight that whether the constraints on investments in the power sector persist or not leads to contrasted trends in energy-GDP decoupling and GHG emissions. Over the short-term, capital scarcity in the power sector constrains the development of energy-intensive activities and therefore leads to higher energy-GDP decoupling. But on the longer-term, constrains on the power sector capacity limits substitution from fossil fuels to electricity, which entails both a low energy-GDP decoupling and a constraint on GDP growth when oil prices are high. The alleviation of suboptimalities appears thus as an insurance policy towards future oil price increase. 相似文献
79.
Leigh N. Fletcher Richard K. Achterberg Glenn S. Orton Amy A. Simon-Miller Sandrine Guerlet F.M. Flasar 《Icarus》2010,208(1):337-352
Five years of thermal infrared spectra from the Cassini Composite Infrared Spectrometer (CIRS) are analyzed to determine the response of Saturn’s atmosphere to seasonal changes in insolation. Hemispheric mapping sequences at 15.0 cm−1 spectral resolution are used to retrieve the variation in the zonal mean temperatures in the stratosphere (0.5-5.0 mbar) and upper troposphere (75-800 mbar) between October 2004 (shortly after the summer solstice in the southern hemisphere) and July 2009 (shortly before the autumnal equinox).Saturn’s northern mid-latitudes show signs of dramatic warming in the stratosphere (by 6-10 K) as they emerge from ring-shadow into springtime conditions, whereas southern mid-latitudes show evidence for cooling (4-6 K). The 40-K asymmetry in stratospheric temperatures between northern and southern hemispheres (at 1 mbar) slowly decreased during the timespan of the observations. Tropospheric temperatures also show temporal variations but with a smaller range, consistent with the increasing radiative time constant of the atmospheric response with increasing pressure. The tropospheric response to the insolation changes shows the largest magnitude at the locations of the broad retrograde jets. Saturn’s warm south-polar stratospheric hood has cooled over the course of the mission, but remains present.Stratospheric temperatures are compared to a radiative climate model which accounts for the spatial distribution of the stratospheric coolants. The model successfully predicts the magnitude and morphology of the observed changes at most latitudes. However, the model fails at locations where strong dynamical perturbations dominate the temporal changes in the thermal field, such as the hot polar vortices and the equatorial semi-annual oscillation (Orton, G., and 27 colleagues [2008]. Nature 453, 196-198). Furthermore, observed temperatures in Saturn’s ring-shadowed regions are larger than predicted by all radiative-climate models to date due to the incomplete characterization of the dynamical response to the shadow. Finally, far-infrared CIRS spectra are used to demonstrate variability of the para-hydrogen distribution over the 5-year span of the dataset, which may be related to observed changes in Saturn’s tropospheric haze in the spring hemisphere. 相似文献
80.
The origin of the martian chaotic terrains is still uncertain; and a variety of geologic scenarios have been proposed. We provide topographic profiles of different chaos landscapes, notably Aureum and Hydraotes Chaos, showing that an initial shallow ground subsidence occurred at the first step of the chaos formation. We infer that the subsidence was caused by intrusion of a volcanic sill; which could have produced consequent melting as well as release of ground water from disrupted aquifer. Signs of a volcanic activity are observed on the floor of Hydraotes Chaos, a complex and deep depression located at the junction of three channels. The volcanic activity is represented by small, 0.5 to 1.5 km diameter, rounded cones with summit pits. The cone's size and morphology, as well as the presence of possible surrounding lava flows, suggest that they are primary volcanic cones similar to terrestrial cinder cones. The identification of volcanic activity on the deepest chaos, where the lower crustal thickness and the faults/fractures system contributed to the magma rising, reveals that magmatic activity, proved by the cones, and possibly help by structural activity, has been a major factor in the formation of chaotic terrains. 相似文献