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41.
Fernando Unrein Inés O’Farrell Irina Izaguirre Rodrigo Sinistro María dos Santos Afonso Guillermo Tell 《Aquatic Sciences - Research Across Boundaries》2010,72(2):179-190
Phosphorus has been traditionally regarded as the controlling nutrient for phytoplankton growth, however, N-limitation is
likely to occur in several environments. For example, nitrogen is considered the main nutrient limiting phytoplankton in floodplain
lakes of the Paraná River basin. However, N2-fixing heterocystous cyanobacteria (N2-cyano) are usually absent in these water bodies. The low pH values frequently found may limit the development of these algae.
We hypothesise that long-term lake isolation allows conspicuous phytoplankton growth during summer, resulting in high photosynthetic
rates and pH. This scenario combined with low DIN (dissolved inorganic nitrogen) would favour the development of N2-cyano. Phytoplankton composition was studied during 16 months in a vegetated and isolated floodplain lake in the Paraná basin.
Additionally, pH was artificially increased in in situ mesocosms to test effects on phytoplankton structure. Lake phytoplankton
was dominated by flagellates (cryptophytes and euglenophytes) and small coccoid algae (chlorophytes and colonial cyanobacteria).
Algal biomass was highest during warm periods. Although pH increased up to 8.8 during the second summer period, N2-cyano remained rare, most likely because of the high DIN concentration recorded. The alkalophilic diatom Cyclotella meneghiniana dominated and was positively correlated with pH. Conversely, PO4= concentrations in the mesocosm experiment were high and DIN remained relatively low. pH enhancement in the treated mesocosms
(avg. pH = 8.2) promoted the development of N2-cyano (Anabaena spp.) and C. meneghiniana, which after 1 month of incubation accounted together for 50% of the biomass in contrast to less than 1.6% in control containers.
Our results support the hypothesis that during the warm season and under low DIN concentration, high pH favours N2-cyano growth in these lakes. We provide new evidence supporting the idea that even under optimal nutrient conditions, N2-cyano do not thrive unless other requirements are satisfied. 相似文献
42.
Axelle Viré Jiansheng Xiang Frank Milthaler Patrick Emmet Farrell Matthew David Piggott John-Paul Latham Dimitrios Pavlidis Christopher Charles Pain 《Ocean Dynamics》2012,62(10-12):1487-1501
Fluid–structure interactions are modelled by coupling the finite element fluid/ocean model ‘Fluidity-ICOM’ with a combined finite–discrete element solid model ‘Y3D’. Because separate meshes are used for the fluids and solids, the present method is flexible in terms of discretisation schemes used for each material. Also, it can tackle multiple solids impacting on one another, without having ill-posed problems in the resolution of the fluid’s equations. Importantly, the proposed approach ensures that Newton’s third law is satisfied at the discrete level. This is done by first computing the action–reaction force on a supermesh, i.e. a function superspace of the fluid and solid meshes, and then projecting it to both meshes to use it as a source term in the fluid and solid equations. This paper demonstrates the properties of spatial conservation and accuracy of the method for a sphere immersed in a fluid, with prescribed fluid and solid velocities. While spatial conservation is shown to be independent of the mesh resolutions, accuracy requires fine resolutions in both fluid and solid meshes. It is further highlighted that unstructured meshes adapted to the solid concentration field reduce the numerical errors, in comparison with uniformly structured meshes with the same number of elements. The method is verified on flow past a falling sphere. Its potential for ocean applications is further shown through the simulation of vortex-induced vibrations of two cylinders and the flow past two flexible fibres. 相似文献
43.
Griselda Chaparro María Soledad Fontanarrosa María Romina Schiaffino Paula de Tezanos Pinto Inés O’Farrell 《Aquatic Sciences - Research Across Boundaries》2014,76(4):579-594
In floodplains located in temperate regions, seasonal variations in temperature affect biological communities and these effects may overlap with those of the flood regime. In this study we explored if and how timing (with regard to temperature seasonality) influences the responses of planktonic and free-floating plants communities to floods in a warm temperate floodplain lake and assessed its relevance for determining state shifts. We took samples of zooplankton, phytoplankton, picoplankton, heterotrophic nanoflagellates and free-floating macrophytes at four sites of the lake characterized by the presence-absence of emergent or free-floating macrophytes along a 2-year period with marked hydrological fluctuations associated to river flood dynamics. We performed ANOVA tests to compare the responses of these communities to floods in cold and warm seasons and among sites. Planktonic communities developed high abundances in response to floods that occurred in the cold season, while the growth of free-floating macrophytes was impaired by low winter temperatures. Spring and summer floods favored profuse colonization by free-floating plants and limited the development of planktonic communities. The prolonged absence of floods during warm periods caused environmental conditions that favored Cyanobacteria growth, leading to a “low turbid waters” regime. The occurrence of floods early in the warm season caused phytoplankton dilution and promoted free-floating plant colonization and a shift towards a “high clear waters” state. Zooplankton:phytoplankton biomass ratio was very low during floods in warm seasons, thus zooplankton grazing on phytoplankton seemed to play a minor role in the maintenance of the clear regime. 相似文献
44.
AJE Healey NJ McKeown WM Potts CL de Beer W Sauer PW Shaw 《African Journal of Marine Science》2017,39(3):307-313
Accurate species identification and biogeographic characterisation are fundamental for appropriate management of expanding cephalopod fisheries. This study addresses this topic within the common cuttlefish Sepia officinalis species complex (S. officinalis, S. hierredda and S. vermiculata), with an emphasis on occurrence in African waters. Tissue samples from the currently presumed distributions of S. vermiculata and S. hierredda (from South Africa and Ghana/Angola, respectively) were sequenced for the cytochrome c oxidase subunit I (COI) and the cytochrome b (cytb) genes of the mitochondrial genome and then compared to existing S. officinalis sequences. Three highly divergent and reciprocally monophyletic clades, corresponding to S. officinalis, S. hierredda and S. vermiculata, were resolved, representing the first molecular confirmation of the distinct species status of S. hierredda and S. vermiculata. The sequences also revealed that, contrary to expectations based on presently published information, all samples from southern Angola were S. vermiculata. These results indicate that the range of S. vermiculata extends beyond the currently described northern limit and that S. hierredda and S. vermiculata may be indiscriminately harvested in Angolan waters. Finer-scale patterns within S. vermiculata phylogeography also indicate that the Benguela Current System and/or other environmental factors serve to isolate northern and southern stocks. 相似文献
45.
On Postglacial Sea Level 总被引:9,自引:0,他引:9
46.
47.
48.
Uranium Removal from Ground Water Using Zero Valent Iron Media 总被引:1,自引:0,他引:1
James Farrell William D. Bostick Robert J. Jarabek Joseph N. Fiedor 《Ground water》1999,37(4):618-624
49.
General Circulation Models (GCMs) are currently used to project future climate. The output of the models is then used to evaluate the effect of a climatic change on resources such as agriculture, forestry, and water resources. The GCMs used in long-term climate studies vary widely in the geographic resolution of their predictions. The approximate matching of resource data to the geographic scale of GCMs is an important step in the evaluation of the effects of climatic change on resources. As gridcell size increases, however, the distribution of resources within cells becomes more heterogeneous, and it becomes more difficult to evaluate the regional effects of climatic change. We quantify the change in resource heterogeneity as a function of gridcell size. Four resource variables (wheat yield, percent forest cover, population density, and percent of land irrigated) are analyzed on the basis of county-averaged data, while assignment to major drainage basins is based on exact watershed boundaries. A major change in resource heterogeneity within gridcells occurs at a grid length of from 1.2° to 3°. 相似文献
50.
Metallic iron filings have been increasingly used in permeable reactive barriers for remediating groundwater contaminated by chlorinated solvents. Understanding solution pH effects on rates of reductive dechlorination in permeable reactive barriers is essential for designing remediation systems that can meet treatment objectives under conditions of varying groundwater properties. The objective of this research was to investigate how the solution pH value affects adsorption of trichloroethylene (TCE) and perchloroethylene (PCE) on metallic iron surfaces. Because adsorption is first required before reductive dechlorination can occur, pH effects on halocarbon adsorption energies may explain pH effects on dechlorination rates. Adsorption energies for trichloroethylene and perchloroethylene were calculated via molecular mechanics simulations using the Universal force field and a self-consistent reaction field charge equilibration scheme. A range in solution pH values was simulated by varying the amount of atomic hydrogen adsorbed on the iron. The potential energies associated trichloroethylene and perchloroethylene complexes were dominated by electrostatic interactions, and complex formation with the surface was found to result in significant electron transfer from the iron to the adsorbed halocarbons. Adsorbed atomic hydrogen was found to lower the energies of trichloroethylene complexes more than those for perchloroethylene. Attractions between atomic hydrogen and iron atoms were more favorable when trichloroethylene versus perchloroethylene was adsorbed to the iron surface. These two findings are consistent with the experimental observation that changes in solution pH affect trichloroethylene reaction rates more than those for perchloroethylene. 相似文献