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221.
The observed distribution of 137Cs resulting from known sources in the Severn Estuary permits the testing of simple predictive models for the one-dimensional distribution of non-conservative substances in an estuary. These models either use a known distribution of salinity to infer corresponding ones for other substances, or else directly solve mass balance equations utilizing previously determined dispersion coefficients. Both methods are shown to previously determined dispersion coefficients. Both methods are shown to provide results comparing favorably with observations.Stokes drift plays an important role in the circulation of the Severn. A modified densimetric Froude number, including this drift, is therefore used to estimate the circulation and stratification of the estuary.A new equation is used for calculating the 137Cs distribution from the observed salinity distribution. It generalizes previous formulations to permit variation of the net runoff with position along the estuary. 相似文献
222.
Crustal and upper mantle S-wave velocity structure beneath the Bransfield Strait (West Antarctica) from regional surface wave tomography 总被引:1,自引:0,他引:1
Regional surface wave tomography in the sub-Antarctic Scotia Sea is helpful in revealing the nature of the crust and the S-wave seismic velocity profile beneath the Bransfield Strait. The joint use of our regional network, global seismographic network stations and local temporary arrays provide better lateral resolution than that obtained in our previous studies concerning the Scotia Sea region.Tomographic analysis of data obtained using 10 broad band seismic stations and more than 300 regional events, shows that the Bransfield Basin is characterised by a strong group velocity reduction of 8% with respect to the surrounding areas, in the period range from 15 s to 50 s.The crustal and upper mantle models of the eastern, central and western Bransfield Basin are obtained by joint inversion of Rayleigh and Love local dispersion curves from 15 s to 50 s. In addition our data set is expanded to a broader period interval (1–80 s), in central Bransfield Strait in order to better constrain the upper mantle and shallow crust.The main results can be summarized as follows: (a) the crust thins distinctly from W toward E; the variation is consistent with the type of volcanism, earthquake distribution and bathymetric observations, (b) low upper mantle velocities (soft lid) extend down to depths exceeding 70 km as a consequence of elevated temperatures, (c) the crust beneath the central Bransfield Basin displays continental characteristics with a gradually increasing S-wave velocity distribution versus depth analogous to the East African Rift structure of Kenya, (d) negative velocity gradients are present in the lower crust beneath the eastern Bransfield Basin; these could be interpreted as magmatic bodies originating from decompression melting of the mantle. 相似文献
223.
Analytical and numerical analysis of pressure drawdown in a poroelastic reservoir with complete overburden effect considered 总被引:1,自引:0,他引:1
Starting from an analytical reservoir model that incorporates full interaction with an elastic overburden, a new hybrid mathematical approach is developed by combining two numerical discretization methods. A tabular reservoir (petroleum reservoir or an aquifer) in an infinite or semi-infinite domain is viewed as a macroscopic displacement discontinuity, allowing use of the efficient displacement discontinuity mathematical method to calculate stresses and displacements that arise because of pressure changes. A 3-D finite element method using a poroelastic formulation is used to discretize the reservoir itself. By coupling the displacement discontinuity and finite element methods, a 3-D large-scale poroelastic reservoir can be simulated within an infinite or semi-infinite domain. The numerical model has been verified through comparison to known solutions, and some time-dependent pressure drawdown problems are analyzed. Results indicate that including the complete overburden (reservoir surroundings) response has a significant effect on pressure drawdown in a poroelastic reservoir during pumping, and should be incorporated in appropriate applications such as well test equations and subsidence analyses. 相似文献
224.
Maurice PARDÉ 《水文科学杂志》2013,58(1):38-51
Abstract Hydrological modelling has faced the problem of ungauged basins for many years: how does one estimate hydrological characteristics for a river for which there are no data? Whatever the kind of model, it needs at least hydroclimatic input data and discharge data for calibration. However, the Yates model does not need any discharge data for calibration: it is a pre-calibrated model from a vegetation—climate classification map. In the specific context of West and Central Africa, where data are often of poor quality and very scarce, it is interesting to compare the performance of such a model with those of calibrated models, and with observed data. For this study, a platform including different semi-global rainfall—runoff models which allow the estimation of monthly runoff at a spatial resolution of 0.5° × 0.5° was used. The performance of the Yates model is very close to those of calibrated models, so that one can say that this simple model, based simply on a vegetation—climate classification, can be a very useful prediction tool in regions of scarce and unreliable data, such as those of interest to the International Association of Hydrological Sciences (IAHS) initiative on prediction in ungauged basins (PUB). Therefore, this model was applied to a period covering the last 30 years, and to a data set covering the first decades of the 21st century, from a climatic scenario of doubling the CO2 concentration in the atmosphere. The results show that, in West Africa, where drought conditions have now prevailed for 35 years, water resources should still be decreasing in the future, following the general decreasing trend of rainfall projected by the climatic scenarios. 相似文献
225.
The potential to use the alkaline residue products fly ash, green liquor dregs, and lime mud originating from paper mills as dry cover materials to seal tailings has been investigated. Metals concentration in lime mud and fly ash had the lowest and highest contents, respectively. The tailings (<1 % sulfur content, primarily pyrite) were disposed about 50 years ago and originated from the former Rönnskär mine site in Sweden. The results of chemical composition analysis show that the raw unoxidized tailings are active toward oxidation, while the components of the adjacent oxidized tailings are not. To quantify the release of metals from the tailings and to evaluate the effect of a sealing layer on oxidation and weathering of the tailings, batch leaching tests were conducted in which leachate from alkaline residue materials was fed to the tailings. The results show that a higher concentration of most trace elements is leached from the unoxidized tailings than from the oxidized tailings. Except As and Cr, the rest of analyzed metals (Cd, Cu, Ni, Pb) became immobilized in response to the increased pH as a consequence of the amendment. The three tested alkaline amendments show a similar potential for preventing the release of metals (with the exception of As and Cr) from the tailings. Under either aerobic or anaerobic conditions, microbial activity was found to be of minor importance. XRD analysis of the field samples revealed that it was feasible to use alkaline residue products in covering tailings, and that it was advantageous to use ash as a cover material more than dregs. 相似文献
226.
Mohammad Z. Al-Hamdan William L. Crosson Sigrid A. Economou Maurice G. Estes Jr Sue M. Estes Sarah N. Hemmings 《国际地球制图》2014,29(1):85-98
We describe a remote sensing and geographic information system (GIS)-based study that has three objectives: (1) characterize fine particulate matter (PM2.5), insolation and land surface temperature (LST) using NASA satellite observations, Environmental Protection Agency (EPA) ground-level monitor data and North American Land Data Assimilation System (NLDAS) data products on a national scale; (2) link these data with public health data from the REasons for Geographic And Racial Differences in Stroke (REGARDS) national cohort study to determine whether these environmental risk factors are related to cognitive decline, stroke and other health outcomes and (3) disseminate the environmental datasets and public health linkage analyses to end users for decision-making through the Centers for Disease Control and Prevention (CDC) Wide-ranging Online Data for Epidemiologic Research (WONDER) system. This study directly addresses a public health focus of the NASA Applied Sciences Program, utilization of Earth Sciences products, by addressing issues of environmental health to enhance public health decision-making. 相似文献
227.
Gordon V. Wolfe Maurice Levasseur Guy Cantin Sonia Michaud 《Deep Sea Research Part I: Oceanographic Research Papers》2000,47(12):687
We adapted the dilution technique to study microzooplankton grazing of algal dimethylsulfoniopropionate (DMSP) vs. Chl a, and to estimate the impact of microzooplankton grazing on dimethyl sulfide (DMS) production in the Labrador Sea. Phytoplankton numbers were dominated by autotrophic nanoflagellates in the Labrador basin, but diatoms and colonial Phaeocystis pouchetii contributed significantly to phytomass at several high chlorophyll stations and on the Newfoundland and Greenland shelfs. Throughout the region, growth of algal Chl a and DMSP was generally high (0.2–1 d−1), but grazing rates were lower and more variable, characteristic of the early spring bloom period. Production and consumption of Chl a vs. DMSP followed no clear pattern, and sometimes diverged greatly, likely because of their differing distributions among algal prey taxa and size class. In several experiments where Phaeocystis was abundant, we observed DMS production proportional to grazing rate, and we found clear evidence of DMS production by this haptophyte following physical stress such as sparging or filtration. It is possible that grazing-activated DMSP cleavage by Phaeocystis contributes to grazer deterrence: protozoa and copepods apparently avoided healthy colonies (as judged by relative growth and grazing rates of Chl a and DMSP), and grazing of Phaeocystis was significant only at one station where cells were in poor condition. Although we hoped to examine selective grazing on or against DMSP-containing algal prey, the dilution technique cannot differentiate selective ingestion and varying digestion rates of Chl a and DMSP. We also found that the dilution method alone was poorly suited for assessing the impact of grazing on dissolved sulfur pools, because of rapid microbial consumption and the artifactual release of DMSP and DMS during filtration. Measuring and understanding the many processes affecting organosulfur cycling by the microbial food web in natural populations remain a technical challenge that will likely require a combination of techniques to address. 相似文献
228.
GeoJournal - Domestic water supply plays a very significant role in the day to day life of humans in the global society and without water, life cannot be continued and that while water provisions... 相似文献