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801.
802.
Mineral carbonation is one of several alternatives for CO2 sequestration and storage. The reaction rates of appropriate minerals with CO2, for instance olivine and serpentine with vast resources, are relatively slow in a CO2 sequestration context and the rates have to be increased to make mineral carbonation a good storage alternative. Increasing the dissolution rate of olivine has been the focus of this paper. Olivine was milled with very high energy intensity using a laboratory planetary mill to investigate the effect of mechanical activation on the Mg extraction potential of olivine in 0.01 M HCl solution at room temperature and pressure. Approximately 30–40% of each sample was dissolved and water samples were taken at the end of each experiment. The pH change was used to calculate time series of the Mg concentrations, which also were compared to the final Mg concentrations in the water samples. Percentage dissolved and the specific reaction rates were estimated from the Mg concentration time series. The measured particle size distributions could not explain the rate constants found, but the specific surface area gave a good trend versus dissolution for samples milled wet and the samples milled with a small addition of water. The samples milled dry had the lowest measured specific surface areas (<4 m2/g), but had the highest rate constants. The crystallinity calculated from X-ray diffractograms, was the material parameter with the best fit for the observed differences in the rate constants. Geochemical modelling of mechanically activated materials indicated that factors describing the changes in the material properties related to the activation must be included. The mechanically activated samples in general reacted faster than predicted by the theoretical models. Mechanical activation as a pre-treatment method was found to enhance the initial specific reaction rates by approximately three orders of magnitude for a sample milled dry for 60 min in a planetary mono mill compared to an unactivated sample. Wet milling in the planetary mill did not produce samples with the same maximum reaction rate as dry milling, but wet milling in general might be easier to implement into a wet carbonation process. Mechanical activation in a planetary mill is likely to consume too much energy for CO2 sequestration purposes, but the increase in obtained olivine rate constants illustrates a potential for using milling as a pre-treatment method. 相似文献
803.
Carbon Cycling and the Coupling Between Proton and Electron Transfer Reactions in Aquatic Sediments in Lake Champlain 总被引:1,自引:0,他引:1
Wei-Jun Cai George W. LutherIII Jeffrey C. Cornwell Anne E. Giblin 《Aquatic Geochemistry》2010,16(3):421-446
We used fine-scale porewater profiles and rate measurements together with a multiple component transport–reaction model to
investigate carbon degradation pathways and the coupling between electron and proton transfer reactions in Lake Champlain
sediments. We measured porewater profiles of O2, Mn2+, Fe2+, HS−, pH and pCO2 at mm resolution by microelectrodes, and profiles of NO3
−, SO4
2−, NH4
+, total inorganic carbon (DIC) and total alkalinity (TA) at cm resolution using standard wet chemical techniques. In addition,
sediment–water fluxes of oxygen, DIC, nitrate, ammonium and N2 were measured. Rates of gross and net sulfate reduction were also measured in the sediments. It is shown that organic matter
(OM) decomposes via six pathways: oxic respiration (35.2%), denitrification (10.4%), MnO2 reduction (3.6%), FeOOH reduction (9.6%), sulfate reduction (14.9%), and methanogenesis (26.4%). In the lake sediments, about
half of the benthic O2 flux is used for aerobic respiration, and the rest is used for the regeneration of other electron acceptors produced during
the above diagenetic reactions. There is a strong coupling between O2 usage and Mn2+ oxidation. MnO2 is also an important player in Fe and S cycles and in pH and TA balance. Although nitrate concentrations in the overlying
water were low, denitrification becomes a quantitatively important pathway for OM decomposition due to the oxidation of NH4
+ to NO3
−. Finally, despite its low concentration in freshwater, sulfate is an important electron acceptor due to its high efficiency
of internal cycling. This paper also discusses quantitatively the relationship between redox reactions and the porewater pH
values. It is demonstrated here that pH and pCO2 are sensitive variables that reflect various oxidation and precipitation reactions in porewater, while DIC and TA profiles
provide effective constraints on the rates of various diagenetic reactions. 相似文献
804.
Joel C. Hoffman Gregory S. Peterson Anne M. Cotter John R. Kelly 《Estuaries and Coasts》2010,33(6):1391-1405
We characterized stable isotope mixing along a river-Great Lake transition zone in the St. Louis River, an important fish
nursery in western Lake Superior, and used it to identify food web linkages supporting young fish production. We observed
a broad, spatial pattern in the carbon stable isotope ratio (δ13C); downriver enrichment in particulate organic carbon and aquatic vegetation δ13C, as well as pelagic, benthic and littoral invertebrate δ13C, reflected isotope mixing along the river-lake transition zone. Fishes with similarly enriched δ13C were used to identify benthopelagic and littoral trophic pathways. River and Lake Superior organic matter (OM) sources contributed
to both pathways. Differences between the δ13C in fishes and invertebrate prey revealed that fish production was supported at multiple spatial scales. The result was that
the food web specific to any location along the transition zone incorporated multiple OM sources from across the watershed. 相似文献
805.
Joanna K. York Gabrielle Tomasky Ivan Valiela Anne E. Giblin 《Estuaries and Coasts》2010,33(5):1069-1079
We measured fluxes of NH4+ and NO3− and δ15N of NH4+, sediment, and porewater NH4+ from incubated sediment cores along a nitrate gradient and in different seasons from Childs River, MA. NH4+ flux was low at the downstream site with the lowest concentration of organic matter (high salinity) but otherwise did not
differ along the estuary. The δ15N of regenerated NH4+ ranged from +6.1‰ to +15.3‰ but did not vary significantly with season or salinity; the mean for the entire estuary was +10.4 ± 0.5‰.
Based on differences between the δ15N of regenerated NH4+ and sediment, and expected isotopic fractionation due to remineralization, we concluded that nitrification occurred after
remineralization of NH4+. Differences between the δ15N of regenerated NH4+ and the δ15N of porewater NH4+ provided further evidence of nitrification. We estimated that 11% to 48% of remineralized NH4+ underwent coupled nitrification–denitrification before release into the water column. In spite of losses to denitrification,
NH4+ flux released 1.4 mol N m−2 year−1 to the water column and could provide 42% of phytoplankton nitrogen requirements. 相似文献
806.
807.
Anne Marie de Grosbois 《Environmental Earth Sciences》2010,60(5):1131-1136
Events
Upcoming international events 相似文献808.
Anne Marie de Grosbois 《Environmental Earth Sciences》2010,60(1):219-224
Events
Upcoming international events 相似文献809.
Steven T. Goldsmith Anne E. Carey Brent M. Johnson Susan A. Welch William H. McDowell 《Geochimica et cosmochimica acta》2010,74(1):85-7854
Recent studies of chemical weathering of andesitic-dacitic material on high-standing islands (HSIs) have shown these terrains have some of the highest observed rates of chemical weathering and associated CO2 consumption yet reported. However, the paucity of stream gauge data in many of these terrains has limited determination of chemical weathering product fluxes. In July 2006 and March 2008, stream water samples were collected and manual stream gauging was performed in watersheds throughout the volcanic island of Dominica in the Lesser Antilles. Distinct wet and dry season solute concentrations reveal the importance of seasonal variations on the weathering signal. A cluster analysis of the stream geochemical data shows the importance of parent material age on the overall delivery of solutes. Observed Ca:Na, HCO3:Na and Mg:Na ratios suggest crystallinity of the parent material may also play an important role in determining weathering fluxes. From total dissolved solids concentrations and mean annual discharge calculations we calculate chemical weathering yields of (6-106 t km−2 a−1), which are similar to those previously determined for basalt terrains. Silicate fluxes (3.1-55.4 t km−2 a−1) and associated CO2 consumption (190-1575 × 103 mol km−2 a−1) determined from our study are among the highest determined to date. The calculated chemical fluxes from our study confirm the weathering potential of andesitic-dacitic terrains and that additional studies of these terrains are warranted. 相似文献
810.
Tabea K. Lissner Anne Holsten Carsten Walther Jürgen P. Kropp 《Climatic change》2012,112(3-4):687-708
The relevance of climate change is especially apparent through the impacts it has on natural and societal systems. A standardised methodology to assess these impacts in order to produce comparable results is still lacking. We propose a semi-quantitative approach to calculate vulnerability to climate change, with the ability to capture complex mechanisms in human-environmental systems. The key mechanisms are delineated and translated into a deterministic graph (impact chain). A fuzzy logic algorithm is then applied to address uncertainty regarding the definition of clear threshold values. We exemplify our approach by analysing the direct impacts of climate change on human health in North Rhine-Westphalia, Germany, where the urban heat island potential, the percentage of elderly population as well as the occurrence of heat waves determine impact intensity. Increases in heatwaves and elderly population will aggravate the impacts. While the influence of climatic changes is apparent on larger spatial scales, societal factors determine the small scale distribution of impacts within our regional case study. In addition to identifying climate change impact hot spots, the structured approach of the impact chain and the methodology of aggregation enable to infer from the results back to the main constituents of vulnerability. Thus, it can provide a basis for decision-makers to set priorities for specific adaptation measures within the complex field of climate change impacts. 相似文献