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271.
Abstract Hydrological models are commonly used to perform real-time runoff forecasting for flood warning. Their application requires catchment characteristics and precipitation series that are not always available. An alternative approach is nonparametric modelling based only on runoff series. However, the following questions arise: Can nonparametric models show reliable forecasting? Can they perform as reliably as hydrological models? We performed probabilistic forecasting one, two and three hours ahead for a runoff series, with the aim of ascribing a probability density function to predicted discharge using time series analysis based on stochastic dynamics theory. The derived dynamic terms were compared to a hydrological model, LARSIM. Our procedure was able to forecast within 95% confidence interval 1-, 2- and 3-h ahead discharge probability functions with about 1.40 m3/s of range and relative errors (%) in the range [–30; 30]. The LARSIM model and the best nonparametric approaches gave similar results, but the range of relative errors was larger for the nonparametric approaches. Editor D. Koutsoyiannis; Associate editor K. Hamed Citation Costa, A.C., Bronstert, A. and Kneis, D., 2012. Probabilistic flood forecasting for a mountainous headwater catchment using a nonparametric stochastic dynamic approach. Hydrological Sciences Journal, 57 (1), 10–25. 相似文献
272.
The effect of surface topography on the lunar photoelectron sheath and electrostatic dust transport 总被引:1,自引:0,他引:1
The dayside near-surface lunar plasma environment is electrostatically complex, due to the interaction between solar UV-induced photoemission, the collection of ambient ions and electrons, and the presence of micron and sub-micron sized dust grains. Further complicating this environment, although less well understood in effect, is the presence of surface relief, typically in the form of craters and/or boulders. It has been suggested that such non-trivial surface topography can lead to complex electrostatic potentials and fields, including “mini-wakes” behind small obstacles to the solar wind flow and “supercharging” near sunlit-shadowed boundaries (Criswell, D.R., De, B.R. [1977]. J. Geophys. Res. 82 (7); De, B.R., Criswell, D.R. [1977]. J. Geophys. Res. 82 (7); Farrell, W.M., Stubbs, T.J., Vondrak, R.R., Delory, G.T., Halekas, J.S. [2007]. Geophys. Res. Lett. 34; Wang, X., Horányi, M., Sternovsky, Z., Robertson, S., Morfill, G.E. [2007]. Geophys. Res. Lett. 34, L16104). In this paper, we present results from a three-dimensional, self-consistent, electrostatic particle-in-cell code used to model the dayside near-surface lunar plasma environment over a variety of local times with the presence of a crater. Additionally, we use the particle-in-cell model output to study the effect of surface topography on the dynamics of electrostatic dust transport, with the goal of understanding previous observations of dust dynamics on the Moon and dust ponding on various asteroids. 相似文献
273.
Mineral deposits frequently contain several elements of interest that are spatially correlated and require the use of joint geostatistical simulation techniques in order to generate models preserving their spatial relationships. Although joint-simulation methods have long been available, they are impractical when it comes to more than three variables and mid to large size deposits. This paper presents the application of block-support simulation of a multi-element mineral deposit using minimum/maximum autocorrelation factors to facilitate the computationally efficient joint simulation of large, multivariable deposits. The algorithm utilized, termed dbmafsim, transforms point-scale spatial attributes of a mineral deposit into uncorrelated service variables leading to the generation of simulated realizations of block-scale models of the attributes of interest of a deposit. The dbmafsim algorithm is utilized at the Yandi iron ore deposit in Western Australia to simulate five cross-correlated elements, namely Fe, SiO2, Al2O3, P and LOI, that are all critical in defining the quality of iron ore being produced. The block-scale simulations reproduce the direct- and cross-variograms of the elements even though only the direct variograms of the service variables have to be modeled. The application shows the efficiency, excellent performance and practical contribution of the dbmafsim algorithm in simulating large multi-element deposits. 相似文献
274.
Alexandre Raphael Cabral Nikola Koglin Ant?nio Augusto Seabra Gomes Bernd Lehmann 《International Journal of Earth Sciences》2012,101(1):377-383
Dissolution cavities in weathered pebbly quartzite of the ~2.5-Ga Moeda Formation at Capanema, Quadrilátero Ferrífero of Minas
Gerais, Brazil, are decorated with suspended filaments of opaline silica. The filaments sustain xenotime–hematite aggregates
in the open space. Xenotime occurs as inclusions in buds and botryoidal aggregates of hematite. The filamentous structures
consist of strand-forming buds, hypha-like extensions, and thin strands that compose mat-like arrangements. They resemble
microbial filaments that were replaced by opaline silica and fossilized. The occurrence of spherical hematite as protuberances
on hematite-free opaline hyphae is interpreted as accretion of dissolved iron onto extracellular polymers. Phosphate sites
in polymeric substances expelled from the microbial filaments might have adsorbed yttrium and heavy rare-earth elements from
groundwater to the iron-accreting polymers. These would have resulted in botryoidal aggregates of hematite with xenotime inclusions.
The presence of authigenic xenotime in the weathering zone opens a new possibility to constrain the evolution of lateritic
profiles by xenotime geochronology. 相似文献
275.
276.
Chen-Chieh Feng Alexandre Sorokine 《International journal of geographical information science》2014,28(6):1294-1315
The paper compares hydrographic and terrain categories in the geospatial data standards of the United States, Taiwan, and Russian Federation where the dominant languages used are from different language families. It aims to identify structural and semantic differences between similar categories across three geospatial data standards. By formalizing the data standard structures and identifying the properties that differentiate sibling categories in each geospatial data standard using well-known formal relations and quality universals, we develop a common basis on which hydrographic and terrain categories in the three data standards can be compared. The result suggests that all the three data standards structure categories with a mixture of relations even though most of them are well-known relations in top-level ontologies. Similar categories can be found across all the three standards. Cases of categories from different standards carrying identical meaning are rare. Partial overlaps in the meaning of the similar categories can be a direct result of different quality universals at work in defining and distinguishing these categories, or in the case of these categories being ordered by size, the threshold values for distinguishing the categories are ambiguous and language-dependent. Understanding these differences avoids incorrect mappings of categories in multilingual applications. More importantly, it provides a starting point for more effective mapping between hydrographic and terrain categories between English, Mandarin, and Russian. 相似文献
277.
Ruitton S Javel F Culioli JM Meinesz A Pergent G Verlaque M 《Marine pollution bulletin》2005,50(10):1061-1068
The introduced green alga Caulerpa racemosa var. cylindracea has been rapidly spreading in the Mediterranean Sea since 1990. It was first observed in France in 1997 (Marseilles). In early 2004, the stretch of the French Mediterranean coastline and the surface area affected by the invasion were estimated at about 83 km and 4014 ha, respectively. The depth range of colonized areas was usually 10-35 m depth. Shallow (0-10 m) and deep (down to 40 m) dense meadows were rarely observed. In contrast to the dead matte of Posidonia oceanica, which constituted the most widely colonized substratum, dense P. oceanica meadows and fine sand with large ripple-marks were not invaded. Few rocky areas were colonized and coarse sand bottoms were usually colonized below 20 m depth. All the colonized areas were exposed to human activities and more than 40% were fishing areas. Mild climate, suitable substrata, presence of vectors of dispersal and absence of efficient biological control make the French Mediterranean coast particularly vulnerable to the further spread of the alga. 相似文献
278.
Laurent Bremond Anne Alexandre Christelle Hly Joël Guiot 《Global and Planetary Change》2005,45(4):277-293
The aim of the study is to calibrate the phytolith index of tree cover density, D/P (the ratio of ligneous dicotyledons phytoliths (D) over Poaceae phytoliths (P)) with Leaf Area Index (LAI) measurements. LAI is the vertically integrated surface of leaves per unit of ground area (m2 leaves/m2 ground). Modern soil samples from southeastern Cameroon, collected along a continuous forest–savanna transect, have been analyzed for phytoliths. Phytolith assemblages and D/P index clearly record the physiognomy of the forest and savanna communities and of the transition between both of them. A highly significant relationship was obtained between D/P and LAI. The relationship between phytolith data and the vegetation transect is also discussed and compared with existing palynological results obtained along the same transect. 相似文献
279.
Rui?SantosEmail author Jo?o?Silva Ana?Alexandre Nuria?Navarro Cristina?Barrón Carlos?M.?Duarte 《Estuaries and Coasts》2004,27(6):977-985
The metabolism and carbon flux in the western sector of the highly dynamic coastal lagoon Ria Formosa (south Portugal) were
assessed to elucidate the relative importance of the contribution of the main communities, the treated sewage inputs from
the adjacent city of Faro, and the exchange with the adjacent coastal waters to the ecosystem metabolism. The results depict
the Ria Formosa as being a highly productive ecosystem dominated by the seagrassZostera noltii. The community dominated by the seagrassCymodocea nodosa had half of the gross production ofZ. noltii, followed by bare sediments and phytoplankton. The net contribution of seagrasses to community metabolism was negligible,
as bothZ. noltii andC. nodosa showed a production: respiration ratio close to 1. Benthic microalgae emerge as the most important components of the net
metabolism. The western sector of Ria Formosa was in metabolic balance during the summer when the study was done. Even though
the total net ecosystem production was 7.22 Kmol C d−1, the error associated with this estimate was 8.38 Kmol C d−1, so ecosystem net production was not significantly different from zero. The Ria Formosa ecosystem is shallow and rapidly
flushed by the tides, which force an important exchange of dissolved organic carbon (DOC) and particulate organic carbon (POC)
with the adjacent coastal waters. The daily net export rate to the adjacent coastal waters, 0.98 Kmol d−1, represented 7.6% of the net ecosystem production, suggesting that the bulk of the net ecosystem production accumulates within
the ecosystem. The organic carbon retention in the western sector of the Ria Formosa is higher than net production, because
the allochthonous carbon inputs from urban sewage enter the carbon mass balance with about 40% of the autochthonous processes,
at about 1.6 Kmol d−1 of DOC and 2.8 Kmol d−1 of POC. The western sector of Ria Formosa has an organic carbon sink of about 46.4 tons per year. Most of this is harvested
in the form of molluscs (clams, cuttlefish, etc.) and fish (sea bream, sea bass, etc.). The total carbon harvested every year
in the form of bivalves is about 40 tons, rendering the Ria Formosa the most productive seafood area in Portugal. 相似文献
280.
Anne Alexandre Isabelle Basile-Doelsch Corinne Sonzogni Claude Parron Fabrice Colin 《Geochimica et cosmochimica acta》2006,70(11):2827-2835
The laser fluorination technique reported here for analyzing the oxygen isotope composition (δ18O) of fine quartz size fractions 50-20, 20-10, 10-5, 5-2, 2-1 and <1 μm has been validated by comparison with the ion microprobe technique. It yields accurate δ18O data with an external precision better than 0.15‰. This is a significant methodological improvement for isotopic studies dealing with materials such as soil or biogenic oxides and silicates: particles are often too small and recovered in insufficient amount to be easily handled for ion microprobe analysis. Both techniques were used to investigate δ18O composition of a Cretaceous quartzite and silcrete sequence from the South-East of France. Quartzite cements average 31.04 ± 1.93‰. They formed from Mid-Cretaceous seawater. Higher in the series, silcretes cements average 26.66 ± 1.36‰. They formed from Upper- or post-Upper-Cretaceous soil water and groundwater. Oxygen isotope data show that the silicification steps from one mineralogical phase to another and from one layer to another (including from an upper pedogenic silcrete to a lower groundwater silcrete) occurred in a closed or weakly evaporating hydrological system. 相似文献