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61.
Sedimentary units generally present anisotropy in their hydraulic properties, with higher hydraulic conductivity along bedding planes, rather than perpendicular to them. This common property leads to a modeling challenge if the sedimentary structure is folded. In this paper, we show that the gradient of the geological potential used by implicit geological modeling techniques can be used to compute full hydraulic conductivity tensors varying in space according to the geological orientation. For that purpose, the gradient of the potential, a vector normal to the bedding, is used to construct a rotation matrix that allows the estimation of the 3D hydraulic conductivity tensor in a single matrix operation. A synthetic 2D cross section example is used to illustrate the method and show that flow simulations performed in such a folded environment are highly influenced by this rotating anisotropy. When using the proposed method, the streamlines follow very closely the folded formation. This is not the case with an isotropic model. 相似文献
62.
Fully probabilistic seismic risk assessment considering local site effects for the portfolio of buildings in Medellín,Colombia 总被引:1,自引:0,他引:1
Mario A. Salgado-Gálvez Daniela Zuloaga-Romero Gabriel A. Bernal Miguel G. Mora Omar-Darío Cardona 《Bulletin of Earthquake Engineering》2014,12(2):671-695
A fully probabilistic seismic risk analysis using a comprehensive approach is conducted for Medellin, the second largest city of Colombia, using a building by building database constructed and complemented from aerial images, considering characteristics such as building use categories, socio-economic levels and replacement values. The seismic hazard used for the analysis corresponds to the most updated study available in the country with the same model that was included in the national building code maps definition. Spectral transfer functions are determined for each of the seismic microzonation zones in order to take into account the dynamic soil response and amplification effects in the risk analysis. Several building types are defined for the city and individual vulnerability functions are assigned to each of them. Risk results are presented in the state of the art metrics such as the loss exceedance curve, probable maximum losses for different return periods, average annual losses and risk maps. The obtained results can be classified by use and socio-economic sectors as well as by structural systems that may help the stakeholders to identify where the risk concentrates. 相似文献
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65.
Jennifer A. Nelson Kathy Licht Catherine Yansa Gabriel Filippelli 《Journal of Paleolimnology》2010,43(1):1-13
Records from lake sediment cores are critical for assessing the relative stability of climate and ecosystems over the Holocene.
Duck Lake in south-central Lower Michigan, USA, was the focus of a study that identified how changes in the geochemical variables
in lake sediments relate to variations in regional climate and local land use during the Holocene. More than 8.5 m of lacustrine
sediment were recovered using Livingston and freeze corers and analyzed for organic carbon, inorganic (carbonate) carbon,
total nitrogen, and trace metals. Repeating packages of sediment (1–10 cm thick) that grade from light (inorganic carbon-rich)
to dark (organic carbon-rich) were found from the surface to a depth of about 8 m. Variations in the high-resolution gray
scale data from core X-radiographs are highly correlated to the relative amount of inorganic carbon. Geochemical analyses
of the upper 8.5 m of sediment revealed a wide range of values: 0.05–10.6% for inorganic carbon (i.e. 0.5–89% calcium carbonate)
and 1.1–28% for organic carbon (i.e. 2.7–70% organic matter). Organic carbon to nitrogen ratios indicate that most of the
sediment organic matter is produced within the lake. A core chronology based on eight AMS radiocarbon dates shows low sediment
accumulation rates (0.05 cm/year) from 10,000 to 3,800 cal year BP and higher sediment accumulation rates (0.1–0.3 cm/year)
from 3,800 cal year BP to present. We suggest that carbonate accumulates during relatively dry times, whereas organic matter
accumulation dominates when nutrient input to the lake is enhanced by wetter climate. The Duck Lake core records a distinct
low point in inorganic carbon deposition that may be related to the 8.2 ka cooling event now documented from several sites
in North America. Spectral analysis of gray scale values shows significant ~200-year periodicities over the past 8,000 years,
hypothesized to result from climate changes induced by solar forcing. Concentrations of trace metals (e.g. lead, iron, copper,
zinc) indicate the onset of regional anthropogenic influence about 150 cal year BP. 相似文献
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Velocity and Temperature Dissimilarity in the Surface Layer Uncovered by the Telegraph Approximation
We consider the Janjic (NCEP Office Note 437:61, 2001) boundary-layer model, which is one of the most widely used in numerical weather prediction models. This boundary-layer model is based on a number of length scales that are, in turn, obtained from a master length multiplied by constants. We analyze the simulation results obtained using different sets of constants with respect to measurements using sonic anemometers, and interpret these results in terms of the turbulence processes in the atmosphere and of the role played by the different length scales. The simulations are run on a virtual machine on the Chameleon cloud for low-wind-speed, unstable, and stable conditions.
相似文献68.
Iqbal Zafar Shahid Shamsuddin Ahmed Kamal Wang Xiaojun Ismail Tarmizi Gabriel Hamza Farooq 《Theoretical and Applied Climatology》2022,148(3-4):1429-1446
Theoretical and Applied Climatology - Satellite-based precipitation (SBP) is emerging as a reliable source for high-resolution rainfall estimates over the globe. However, uncertainty in SBP is... 相似文献
69.
A 7000-year record of local fire history was reconstructed from three ombrotrophic peatlands in the James Bay lowlands (northwestern Québec, Canada) using a high-resolution analysis of macroscopic charcoal (long axis ≥ 0.5 mm). The impact of fire on vegetation changes was evaluated using detailed analysis of plant macrofossils. Compared to upland boreal forest, fire incidence in these Sphagnum-dominated bogs is rather low. Past fire occurrence seems to have been controlled primarily by internal processes associated with local hydroseral succession. Size of the peatland basin and distance from the well-drained forest soils also appear to be factors controlling fire occurrence. The impact of peatland fires on long-term vegetation succession appears negligible except in a forested bog, where it initiated the replacement of Sphagnum by mosses. In some circumstances, fire caused marked changes in the bryophyte assemblages over many decades. However, ombrotrophic peatland vegetation is generally resilient to surface fire. 相似文献
70.
The transport of chemically reactive solutes (e.g. surfactants, CO2 or dissolved minerals) is of fundamental importance to a wide range of applications in oil and gas reservoirs such as enhanced
oil recovery and mineral scale formation. In this work, we investigate exponential time integrators, in conjunction with an
upwind weighted finite volume discretisation in space, for the efficient and accurate simulation of advection–dispersion processes
including non-linear chemical reactions in highly heterogeneous 3D oil reservoirs. We model sub-grid fluctuations in transport
velocities and uncertainty in the reaction term by writing the advection–dispersion–reaction equation as a stochastic partial
differential equation with multiplicative noise. The exponential integrators are based on the variation of constants solution
and solve the linear system exactly. While this is at the expense of computing the exponential of the stiff matrix representing
the finite volume discretisation, the use of real Léja point or the Krylov subspace technique to approximate the exponential
makes these methods competitive compared to standard finite difference-based time integrators. For the deterministic system,
we investigate two exponential time integrators, the second-order accurate exponential Euler midpoint (EEM) scheme and exponential
time differencing of order one (ETD1). All our numerical examples demonstrate that our methods can compete in terms of efficiency
and accuracy compared with standard first-order semi-implicit time integrators when solving (stochastic) partial differential
equations that model mixing and chemical reactions in 3D heterogeneous porous media. Our results suggest that exponential
time integrators such as the ETD1 and EEM schemes could be applied to typical 3D reservoir models comprising tens to hundreds
of thousands unknowns. 相似文献