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121.
The species of Ophiuroidea that commonly occur on coral reefs can be found on different substrates and associated with other organisms including algae, sponges, and corals. This study evaluated the temporal variability of the ophiuroid fauna associated with the alga Amphiroa fragilissima on the Ponta Verde coral reef on the coast of Maceió in Alagoas, Northeastern Brazil. Replicate samples of algal substrate were collected at low tide during in the dry and rainy seasons, over a 10‐year period, from 1998–2007. Eight species of Ophiuroidea were identified, with a total of 8736 individuals associated with A. fragilissima. The most dominant and frequent species of Ophiuroidea were Amphipholis squamata and Ophiactis savignyi; all other species were rare. Cluster analysis and nMDS detected four groups, with two groups each occurring only in summer or winter periods, as well as other groups occurring in both periods. 相似文献
122.
Monica Riva Alberto Guadagnini Shlomo P. Neuman Emanuela Bianchi Janetti Bwalya Malama 《Advances in water resources》2009
We present a nonlinear stochastic inverse algorithm that allows conditioning estimates of transient hydraulic heads, fluxes and their associated uncertainty on information about hydraulic conductivity (K) and hydraulic head (h ) data collected in a randomly heterogeneous confined aquifer. Our algorithm is based on Laplace-transformed recursive finite-element approximations of exact nonlocal first and second conditional stochastic moment equations of transient flow. It makes it possible to estimate jointly spatial variations in natural log-conductivity (Y=lnK), the parameters of its underlying variogram, and the variance–covariance of these estimates. Log-conductivity is parameterized geostatistically based on measured values at discrete locations and unknown values at discrete “pilot points”. Whereas prior values of Y at pilot point are obtained by generalized kriging, posterior estimates at pilot points are obtained through a maximum likelihood fit of computed and measured transient heads. These posterior estimates are then projected onto the computational grid by kriging. Optionally, the maximum likelihood function may include a regularization term reflecting prior information about Y. The relative weight assigned to this term is evaluated separately from other model parameters to avoid bias and instability. We illustrate and explore our algorithm by means of a synthetic example involving a pumping well. We find that whereas Y and h can be reproduced quite well with parameters estimated on the basis of zero-order mean flow equations, all model quality criteria identify the second-order results as being superior to zero-order results. Identifying the weight of the regularization term and variogram parameters can be done with much lesser ambiguity based on second- than on zero-order results. A second-order model is required to compute predictive error variances of hydraulic head (and flux) a posteriori. Conditioning the inversion jointly on conductivity and hydraulic head data results in lesser predictive uncertainty than conditioning on conductivity or head data alone. 相似文献
123.
Joint Inversion of Body-Wave Arrival Times and Surface-Wave Dispersion for Three-Dimensional Seismic Structure Around SAFOD 总被引:2,自引:0,他引:2
Haijiang Zhang Monica Maceira Philippe Roux Clifford Thurber 《Pure and Applied Geophysics》2014,171(11):3013-3022
We incorporate body-wave arrival time and surface-wave dispersion data into a joint inversion for three-dimensional P-wave and S-wave velocity structure of the crust surrounding the site of the San Andreas Fault Observatory at Depth. The contributions of the two data types to the inversion are controlled by the relative weighting of the respective equations. We find that the trade-off between fitting the two data types, controlled by the weighting, defines a clear optimal solution. Varying the weighting away from the optimal point leads to sharp increases in misfit for one data type with only modest reduction in misfit for the other data type. All the acceptable solutions yield structures with similar primary features, but the smaller-scale features change substantially. When there is a lower relative weight on the surface-wave data, it appears that the solution over-fits the body-wave data, leading to a relatively rough V s model, whereas for the optimal weighting, we obtain a relatively smooth model that is able to fit both the body-wave and surface-wave observations adequately. 相似文献
124.
Christopher S. Romanek Concepcin Jimnez-Lpez Alejandro Rodriguez Navarro Monica Snchez-Romn Nita Sahai Max Coleman 《Geochimica et cosmochimica acta》2009,73(18):5361-5376
A set of free-drift experiments was undertaken to synthesize carbonates of mixed cation content (Fe, Ca, Mg) from solution at 25 and 70 °C to better understand the relationship between the mineralogy and composition of these phases and the solutions from which they precipitate. Metastable solid solutions formed at 25 °C which are not predicted from the extrapolation of higher temperature equilibrium assemblages; instead, solids formed that were intermediary in chemical composition to known magnesite–siderite and dolomite solid solutions. A calcite–siderite solid solution precipitated at 25 °C, with the percentage of CaCO3 in the solid being proportional to the aqueous Ca/Fe ratio of the solution, while Mg was excluded from the crystal structure except at relatively high aqueous Mg/Ca and Mg/Fe ratios and a low Ca content. Alternatively, at 70 °C Mg was the predominant cation of the solid solutions. These results are compatible with the hypothesis that the relative dehydration energies of Fe, Ca and Mg play an important role in the formation of mixed cation carbonates in nature. 相似文献
125.
通过若干实例,本文讨论了地磁数据分析中的一些方法.这些方法包括时间序列的多项式拟合,相关性分析,频谱分析和小波分析等.在Matlab和AutoSignal软件下实现了以上方法,并基于这些方法研究了地磁场形态和地磁现象的频谱特征.我们分析了Surlari观测台(余纬45.3°,经度26.3°)的地磁时间序列,并与Ottawa(余纬44.6°,〖JP2〗经度284.5°),Canberra(余纬125.3°,经度149.3°), Kakioka(余纬53.8°,经度140.2°),Vernadsky〖JP〗(余纬155.3°,经度295.7°)等台站的结果进行了对比分析,讨论了Fourier变换时间窗和小波基函数选取的影响,有限长时间序列引起的边缘效应,以及小波尺度和Fourier频率的关系等问题.我们采用谱分析和小波分析处理了2007年两个台站的地磁数据,研究了地磁场形态和地磁现象的频谱特征,并讨论了Fourier变换和小波变换的优缺点. 相似文献
126.
Effects of uncertainty of lithofacies, conductivity and porosity distributions on stochastic interpretations of a field scale tracer test 总被引:2,自引:2,他引:0
Monica Riva Laura Guadagnini Alberto Guadagnini 《Stochastic Environmental Research and Risk Assessment (SERRA)》2010,24(7):955-970
We investigate the importance of selecting two different methodologies for the determination of hydraulic conductivity from
available grain-size distributions on the stochastic modeling of the depth-averaged breakthrough curve observed during a forced-gradient
tracer test experiment. The latter was performed in the Lauswiesen alluvial aquifer, located near the city of Tübingen, Germany,
by injecting NaBr into a well at a distance of about 50 m from a pumping well. We also examine the joint effect of the choice
of the transport model adopted to describe solute transport at the site and the way the spatial distribution of porosity is
assessed. In the absence of direct measurements of porosity, we consider: (a) the model used by Riva et al. (J Contam Hydrol
88:92–118, 2006; J Contam Hydrol 101:1–13, 2008), which relates the natural logarithms of effective porosity and conductivity through an empirical, experimentally-based,
linear relationship derived for a nearby experimental site; and (b) a model based on a commonly used relationship linking
the total porosity to the coefficient of uniformity of grain size distributions. Transport is described in terms of a purely
advective process and/or by including mass exchange processes between mobile and immobile regions. Modeling of flow and transport
is performed within a Monte Carlo framework, upon conceptualizing the aquifer as a random composite medium. Our results indicate
that the model adopted to describe the correlation between conductivity and porosity and the way grain-sieve information are
incorporated to depict the heterogeneous distribution of hydraulic conductivity can have relevant effects in the interpretation
of the data at the site. All the conceptual models employed to describe the structural heterogeneity of the system and transport
features can reasonably reproduce the global characteristics of the experimental depth-averaged breakthrough curve. Specific
details, such as the peak concentration and the time of first arrival, can be better reproduced by a double porosity transport
model when a correlation between conductivity and porosity based on grain size information at the site is considered. The
best prediction of the late-time behavior of the measured breakthrough curves, in terms of the observed heavy tailing, is
offered by directly linking porosity distribution to the spatial variability of particle size information. 相似文献
127.
The Eberswalde crater and its contributing basins have been analyzed in detail in order to reconstruct the geological evolution of the water-related landforms with particular focus on the Eberswalde delta-like feature. Based on a complex strata organization characterized by a topset-foreset-bottomset geometry, typical of delta progradation on Earth, we interpret the Eberswalde feature to be a fan delta associated with a lacustrine system. Depositional sub-environments have been recognized and mapped and the sedimentary processes discussed. A sequence stratigraphy approach has been used to evaluate the system, which we interpret to result from three depositional sequences. These sequences suggest relative water level fluctuations and a longer trend over time towards decreasing water content inside the basin. 相似文献
128.
129.
Mara Monica Tiberti Stefano Lorito Roberto Basili Vanja Kastelic Alessio Piatanesi Gianluca Valensise 《Pure and Applied Geophysics》2008,165(11-12):2117-2142
We calculated the expected impact on the Italian coast of the Adriatic Sea of a large set of tsunamis resulting from potential earthquakes generated by major fault zones. Our approach merges updated knowledge on the regional tectonics and scenario-like calculations of expected tsunami impact. We selected six elongated potential source zones. For each of them we determined a Maximum Credible Earthquake and the associated Typical Fault, described by its size, geometry and kinematics. We then let the Typical Fault float along strike of its parent source zone and simulated all tsunamis it could generate. Simulations are based on the solution of the nonlinear shallow water equations through a finite-difference technique. For each run we calculated the wavefields at specified simulation times and the maximum water height field (above mean sea level), then generated travel-time maps and maximum water height profiles along the target coastline. Maxima were also classified in a three-level code of expected tsunami threat. We found that the southern portion of Apulia facing Albania and the Gargano promontory are especially prone to the tsunami threat. We also found that some bathymetric features are crucial in determining the focalization-defocalization of tsunami energy. We suggest that our results be taken into account in the design of early-warning strategies. 相似文献
130.
When the earth blisters: Exploring recurrent liquefaction features in the coastal system of Christchurch,New Zealand 下载免费PDF全文
Monica Giona Bucci Peter Almond Pilar Villamor William Ries Carol Smith Martitia Tuttle 《地学学报》2017,29(3):162-172
The 14 February, or Valentine's Day, 2016 earthquake located offshore of Christchurch produced a new generation of liquefaction in the coastal environment of Christchurch, an environment of recurrent liquefaction during the 2010–2011 Canterbury Earthquake Sequence. The Valentine's Day earthquake occurred while trenches were open at a site in the coastal environment for studying the 2010–2011 liquefaction features. Observations in the 2016 trenches provided insights into the formation of a suite of surface and subsurface liquefaction features characteristic of the dune deposits, related to the persistent shallow water table, well‐sorted sands within the liquefiable layer and the soil above. Given these conducive conditions, there is a high potential that all earthquakes capable of inducing liquefaction may have been recorded during formation of the dunes near Christchurch. However, overprinting by subsequent generations of liquefaction features may be common and present challenges in unravelling the event history. 相似文献