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排序方式: 共有369条查询结果,搜索用时 234 毫秒
61.
Chukanov Nikita V. Zubkova Natalia V. Jančev Simeon Pekov Igor V. Ermolaeva Vera N. Varlamov Dmitry A. Belakovskiy Dmitriy I. Britvin Sergey N. 《Mineralogy and Petrology》2020,114(2):129-140
Mineralogy and Petrology - This paper describes specific features of isomorphism of unusual amphiboles containing up to 23 wt% ZnO and up to 1.3 wt% CuO from sulfide-free... 相似文献
62.
Vera M. van Beek Bryant A. Robbins Gijs J.C.M. Hoffmans Adam Bezuijen Leo C. van Rijn 《国际泥沙研究》2019,34(5):401-408
Backward erosion piping involves the gradual removal of granular material under the action of water flow from the foundation of a dam or levee, whereby shallow pipes are formed that grow in the direction opposite to the flow. This pipe-forming process can ultimately lead to failure of a water-retaining structure and is considered one of the most important failure mechanisms for dikes and levees in the Netherlands and the United States. Modeling of this mechanism requires the assessment of hydraulic conditions in the pipe, which are controlled by the particle equilibrium at the pipe wall. Since the pipe's dimensions are controlled by the inflow to the pipe from the porous medium, the flow through the pipe is thought to be laminar for fine- to medium-grained sands. The literature provides data for incipient motion in laminar flow, which is reviewed here and complemented with data from backward erosion experiments. The experiments illustrate the applicability of the laminar incipient motion data to determine the erosion pipe dimensions and corresponding pipe hydraulics for fine- to medium-grained sands, for the purpose of backward erosion piping modeling. 相似文献
63.
Water Resources - Groundwater performs an important role in the territory of the plains Garmsar. In this study, on the basis of water samples, which were obtained from the wells of the region,... 相似文献
64.
Leonardo de Magalhães Natália Pessoa Noyma Luciana Lima Furtado Maíra Mucci Frank van Oosterhout Vera L. M. Huszar Marcelo Manzi Marinho Miquel Lürling 《Estuaries and Coasts》2017,40(1):121-133
Eutrophication is considered the most important water quality problem in freshwaters and coastal waters worldwide promoting frequent occurrence of blooms of potentially toxic cyanobacteria. Removal of cyanobacteria from the water column using a combination of coagulant and ballast is a promising technique for mitigation and an alternative to the use of algaecides. In laboratory, we tested experimentally the efficiency of two coagulants, polyaluminium chloride (PAC) and chitosan (made of shrimp shells), alone and combined with two ballasts: red soil (RS) and the own lagoon sediment, to remove natural populations of cyanobacteria, from an urban brackish coastal lagoon. PAC was a very effective coagulant when applied at low doses (≤8 mg Al L?1) and settled the cyanobacteria, while at high doses (≥16 mg Al L?1) large flocks aggregated in the top of test tubes. In contrast, chitosan was not able to form flocks, even in high doses (>16 mg L?1) and did not efficiently settle down cyanobacteria when combined with ballast. The RS itself removed 33–47 % of the cyanobacteria. This removal was strongly enhanced when combined with PAC in a dose-dependent matter; 8 mg Al L?1 was considered the best dose to be applied. The lagoon sediment alone did not promote any settling of cyanobacteria but removal was high when combined with PAC. Combined coagulant and ballast seems a very efficient, cheap, fast and safe curative measure to lessen the harmful cyanobacteria bloom nuisance in periods when particularly needed, such as around the 2016 Olympics in Jacarepaguá Lagoon. 相似文献
65.
Christopher J. Daly Karin R. Bryan Mauricio R. Gonzalez Antonio H. F. Klein Christian Winter 《Ocean Dynamics》2014,64(6):863-877
In order to decrease the simulation time of morphodynamic models, often-complex wave climates are reduced to a few representative wave conditions (RWC). When applied to embayed beaches, a test of whether a reduced wave climate is representative or not is to see whether it can recreate the observed equilibrium (long-term averaged) bathymetry of the bay. In this study, the wave climate experienced at Milagro Beach, Tarragona, Spain was discretized into ‘average’ and ‘extreme’ RWCs. Process-based morphodynamic simulations were sequenced and merged based on ‘persistent’ and ‘transient’ forcing conditions, the results of which were used to estimate the equilibrium bathymetry of the bay. Results show that the effect of extreme wave events appeared to have less influence on the equilibrium of the bay compared to average conditions of longer overall duration. Additionally, the persistent seasonal variation of the wave climate produces pronounced beach rotation and tends to accumulate sediment at the extremities of the beach, rather than in the central sections. It is, therefore, important to account for directional variability and persistence in the selection and sequencing of representative wave conditions as is it essential for accurately balancing the effects beach rotation events. 相似文献
66.
Danny Arroyo Daniel García Mario Ordaz Mauricio Alexander Mora Shri Krishna Singh 《Journal of Seismology》2010,14(4):769-785
We derive strong ground-motion relations for horizontal components of pseudo-acceleration response spectra from Mexican interplate
earthquakes at rock sites (NEHRP B class) in the forearc region. The functional form is obtained from the analytical solution
of a circular finite-source model. For the regression analysis we use a recently proposed multivariate Bayesian technique.
The resulting model has similar accuracy as those models derived from regional and worldwide subduction-zone databases. However,
there are significant differences in the estimations computed from our model and other models. First, our results reveal that
attenuation in Mexico tends to be stronger than that of worldwide relations, especially for large events. Second, our model
predicts ground motions for large earthquakes at close distances to the source that are considerably larger than the estimations
of global models. Lack of data in this range makes it difficult to identify the most appropriate model for this scenario.
Nevertheless, according to the available data at the city of Acapulco, our model seems to estimate seismic hazard more adequately
than the other models. These new relations may be useful in computing seismic hazard for the Mexican forearc region, where
no similar equations had been yet proposed. 相似文献
67.
Vera D’Amico Dario Albarello Ragnar Sigbjörnsson Rajesh Rupakhety 《Bulletin of Earthquake Engineering》2016,14(7):1797-1811
We present the results of probabilistic seismic hazard assessment for Iceland in the framework of the EU project UPStrat-MAFA using the so-called site approach implemented in the SASHA computational code. This approach estimates seismic hazard in terms of macroseismic intensity by basically relying on local information about documented effects of past seismic events in the framework of a formally coherent and complete treatment of intensity data. In the case of Iceland, due to the lack of observed intensities for past earthquakes, local seismic histories were built using indirect macroseismic estimates deduced from epicentral information through an empirical attenuation relationship in probabilistic form. Seismic hazard was computed for four exceedance probabilities for an exposure time of 50 years, equivalent to average return periods of 50, 200, 475 and 975 years. For some localities, further return periods were examined and deaggregation analysis was performed. Results appear significantly different from previous seismic hazard maps, though just a semi-qualitative comparison is possible because of the different shaking measure considered (peak ground acceleration versus intensity), and the different computational methodology and input data used in these studies. 相似文献
68.
69.
70.
Assessing future risk: quantifying the effects of sea level rise on storm surge risk for the southern shores of Long Island, New York 总被引:2,自引:1,他引:1
Christine C. Shepard Vera N. Agostini Ben Gilmer Tashya Allen Jeff Stone William Brooks Michael W. Beck 《Natural Hazards》2012,60(2):727-745
Sea level rise threatens to increase the impacts of future storms and hurricanes on coastal communities. However, many coastal
hazard mitigation plans do not consider sea level rise when assessing storm surge risk. Here we apply a GIS-based approach
to quantify potential changes in storm surge risk due to sea level rise on Long Island, New York. We demonstrate a method
for combining hazard exposure and community vulnerability to spatially characterize risk for both present and future sea level
conditions using commonly available national data sets. Our results show that sea level rise will likely increase risk in
many coastal areas and will potentially create risk where it was not before. We find that even modest and probable sea level
rise (.5 m by 2080) vastly increases the numbers of people (47% increase) and property loss (73% increase) impacted by storm
surge. In addition, the resulting maps of hazard exposure and community vulnerability provide a clear and useful example of
the visual representation of the spatial distribution of the components of risk that can be helpful for developing targeted
hazard mitigation and climate change adaptation strategies. Our results suggest that coastal agencies tasked with managing
storm surge risk must consider the effects of sea level rise if they are to ensure safe and sustainable coastal communities
in the future. 相似文献