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71.
72.
Sousa OV Macrae A Menezes FG Gomes NC Vieira RH Mendonça-Hagler LC 《Marine pollution bulletin》2006,52(12):1725-1734
The effects of shrimp farm effluents on bacterial communities in mangroves have been infrequently reported. Classic and molecular biology methods were used to survey bacterial communities from four mangroves systems. Water temperature, salinity, pH, total heterotrophic bacteria and maximum probable numbers of Vibrio spp. were investigated. Genetic profiles of bacterial communities were also characterized by polymerase chain reaction (PCR) amplification of eubacterial and Vibrio 16S rDNA using denaturing gradient gel electrophoresis (DGGE). Highest heterotrophic counts were registered in the mangrove not directly polluted by shrimp farming. The Enterobacteriaceae and Chryseomonas luteola dominated the heterotrophic isolates. Vibrio spp. pathogenic to humans and shrimps were identified. Eubacterial genetic profiles suggest a shared community structure independent of mangrove system. Vibrio genetic profiles were mangrove specific. Neither microbial counts nor genetic profiling revealed a significant decrease in species richness associated with shrimp farm effluent. The complex nature of mangrove ecosystems and their microbial communities is discussed. 相似文献
73.
Stereospondyls survived the Permo-Triassic extinctions in a refuge probably located in the landmass that nowadays comprises Australia. Subsequently, they radiated to other parts of Pangaea, reaching their highest distribution and diversification during the Early Triassic. An incomplete interclavicle from the Caturrita Formation represents their first record in the Upper Triassic of Brazil. Previously, Upper Triassic South American stereospondyls were restricted to Argentina. This new record reinforces a former hypothesis that suggests the presence of a more diverse stereospondyl fauna in South America during the Late Triassic than previously assumed. Additionally, the presence of a stereospondyl and a phytosaur in the Caturrita Formation reinforces the hypothesis of a change to more humid climatic conditions in the Paraná Basin during the Upper Triassic. The record of Early Triassic stereospondyls in South America suggests that they first colonized Brazil and/or Uruguay, spreading from South Africa during the Early Triassic, subsequently reaching Argentina. Up till now, there is no record of Middle Triassic stereospondyls in either Argentina and Brazil, probably due to either taphonomic bias or insufficient prospecting. Despite the lack of direct evidence, one should not dismiss an earlier stereospondyl colonization of Argentina still during the Early or Middle Triassic. 相似文献
74.
Encarnación Roda-Robles Romeu Vieira Alfonso Pesquera Alexandre Lima 《Mineralogy and Petrology》2010,100(1-2):23-34
Granitic pegmatites are widespread within a schist-metagreywacke complex in the Fregeneda-Almendra area (Central Iberian Zone). They intrude pre-Ordovician metasedimentary rocks and show a zonal distribution relative to the Meda-Penedono-Lumbrales granitic complex, from barren bodies to those enriched in Li, F, Sn, Nb>Ta, P and Be. Based on mineralogical criteria, these pegmatites are classified into three main categories: barren, intermediate and rare-element pegmatites, with each type including various subtypes. Phosphates are present in many pegmatites that usually occur as fine-grained accessory minerals. The most complex association of such minerals includes numerous Fe–Mn phosphates that occur in intermediate pegmatites. Al-phosphates are characteristic of Li-rich pegmatites. Electron microprobe analyses of representative phosphates reflect compositional differences depending on the pegmatite type. The Fe/(Fe+Mn) ratio of phosphates tends to decrease as the evolution degree of the pegmatites increases. 相似文献
75.
Variability of the gas transfer velocity of CO<Subscript>2</Subscript> in a macrotidal estuary (the Scheldt) 总被引:1,自引:0,他引:1
Alberto?Vieira?BorgesEmail author Jean-Pierre?Vanderborght Laure-Sophie?Schiettecatte Frédéric?Gazeau Sarah?Ferrón-Smith Bruno?Delille Michel?Frankignoulle 《Estuaries and Coasts》2004,27(4):593-603
We report a large set of 295 interfacial carbon dioxide (CO2) flux measurements obtained in the Scheldt estuary in November 2002 and April 2003, using the floating chamber method. From
concomitant measurements of the air-water CO2 gradient, we computed the gas transfer velocity of CO2. The gas transfer velocity is well correlated to wind speed and a simple linear regression function gives the most consistent
fit to the data. Based on water current measurements, we estimated the contribution of water current induced turbulence to
the gas transfer velocity, using the conceptual relationship of O'Connor and Dobbins (1958). This allowed us to construct
an empirical relationship to compute the gas transfer velocity of CO2 that accounts for the contribution of wind and water current. Based on this relationship, the spatial and temporal variability
of the gas transfer velocity in the Scheldt estuary was investigated. Water currents contribute significantly to the gas transfer
velocity, but the spatial and temporal variability (from daily to seasonal scales) is mainly related to wind speed variability. 相似文献
76.
High-pressure minerals in mafic microgranular enclaves: evidences for co-mingling between lamprophyric and syenitic magmas at mantle conditions 总被引:1,自引:1,他引:0
Jorge?Plá CidEmail author Lauro?Valentim?Stoll?Nardi Larissa?Zitto?Stabel R?mmulo?Vieira?Concei??o Naira?Maria?Balzaretti 《Contributions to Mineralogy and Petrology》2003,145(4):444-459
Mafic microgranular enclaves, composed of diopside and rare magnesium biotite phenocrysts in a groundmass of diopside, biotite, apatite, Fe-Ti-oxides, and alkali feldspar, are associated with Neoproterozoic Piquiri potassic syenite in southern Brazil. Co-genetic mica and clinopyroxene cumulates present inclusions of pyrope-rich garnet in diopside phenocrysts. Textural evidence, as well as the chemical and mineralogical composition, suggest that enclaves crystallized from a lamprophyric magma and co-mingled with the host syenitic magma. The contrasting temperature between both magmas and the consequent chilling was important for the preservation of some early-crystallized minerals in the mafic magma. Diopside groundmass grains contain micro-inclusions of K-rich augite and phlogopite, and some clinopyroxene phenocrysts and elongate groundmass crystals have potassium-rich cores. The pyrope-rich garnet have high #mg number (67–68), with appreciable amounts of Na2O and K2O comparable to pyrope synthesized at 5 GPa. The extremely high K2O contents of K-rich augite micro-inclusions suggest non-equilibrium with the parental magma, whereas the other K-rich clinopyroxenes are similar to K-clinopyroxenes produced at 5–6 GPa. K-clinopyroxene and garnet in mafic microgranular enclaves suggest that lamprophyric magma started its crystallization at upper mantle conditions, and chilled clinopyroxenes with measurable amounts of K2O are taken as evidence that co-mingling began still at mantle pressures. 相似文献
77.
Frédéric Gazeau Jean-Pierre Gattuso Jack J. Middelburg Natacha Brion Laure-Sophie Schiettecatte Michel Frankignoulle Alberto Vieira Borges 《Estuaries and Coasts》2005,28(6):868-883
Planktonic gross primary production (GPP), community respiration (CR), and nitrification (NIT) were measured monthly in the
Scheldt estuary by the oxygen incubation method in 2003. No significant evolution of planktonic GPP was observed since the
1990s with high rates in the freshwater area (salinity 0; 97±65 mmol C m−2 d−1) decreasing seaward (22–37 mmol C m−2 d−1). A significant decrease of NIT was observed with regard to previous investigations although this process still represents
up to 20% of total organic matter production in the inner estuary. Planktonic CR was highest in the inner estuary and seemed
to be mainly controlled by external organic matter inputs. Planktonic net community production was negative most of the time
in the estuary with values ranging from −300 to 165 mmol C m−2 d−1. Whole estuary net ecosystem production (NEP) was investigated on an annual scale using the results mentioned above and published
benthic metabolic rates. A NEP of −39±8 mmol C m−2 d−1 was estimated, which confirms the strong heterotrophic status of this highly nutrified estuary. NEP rates were computed from
June to December 2003 to compare with results derived from the Land-Ocean Interaction in the Coastal Zone budgeting procedure
applied to dissolved inorganic phosphorus and carbon (DIP and DIC). DIP budgets failed to provide realistic estimates in the
inner estuary where abiotic processes account for more than 50% of the nonconservative DIP flux. DIC budgets predicted a much
lower NEP than in situ incubations (−109±31 versus −42±9 mmol C m−2 d−1) although, as each approach is associated with several critical assumptions, the source of this discrepancy remains unclear. 相似文献
78.
Using a genetic algorithm for 3-D inversion of gravity data in Fuerteventura (Canary Islands) 总被引:2,自引:0,他引:2
The use of genetic algorithms in geophysical inverse problems is a relatively recent development and offers many advantages in dealing with the non-linearity inherent in such applications. We have implemented a genetic algorithm to efficiently invert a set of gravity data. Employing several fixed density contrasts, this algorithm determines the geometry of the sources of the anomaly gravity field in a 3-D context. The genetic algorithms, based on Darwins theory of evolution, seek the optimum solution from an initial population of models, working with a set of parameters by means of modifications in successive iterations or generations. This searching method traditionally consists of three operators (selection, crossover and mutation) acting on each generation, but we have added a further one, which smoothes the obtained models. In this way, we have designed an efficient inversion gravity method, confirmed by both a synthetic example and a real data set from the island of Fuerteventura. In the latter case, we identify crustal structures related to the origin and evolution of the island. The results show a clear correlation between the sources of gravity field in the model and the three volcanic complexes recognized in Fuerteventura by other geological studies. 相似文献
79.
A gravimetric survey, covering a site 200 m square, was carried out in order to locate karstic cavities. After eliminating the regional trend using a polynomial fit, the residual is modelled by least-squares prediction. Correlated signals for several wavelengths are detected. The inversion of these anomalies is performed by a global 3D adjustment using spherical bodies as models. The adjustment is repeated in order to obtain a stable configuration. The results show the probable presence of a system of cavities and galleries. Data collected from boreholes and the subsequent appearance of sink-holes are consistent with the results. 相似文献
80.
J. H. Daluz Vieira 《Journal of Hydrology》1983,60(1-4):43-58
The solutions of the Saint-Vénant equations are compared with those of the kinematic, diffusion and gravity wave approximations, for a range of constant Froudé and kinematic wave numbers, with two different lower boundary conditions: (1) critical flow; and (2) zero depth gradient. For each lower boundary condition, zones are defined in the F0,k-field in which either kinematic, diffusion or gravity wave solutions may be used to approximate the full Saint-Vénant solutions. 相似文献