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341.
Existing methods of cosmogenic nuclide burial dating perform well provided that sediment sources undergo steady rates of erosion and the samples experience continuous exposure to cosmic rays. These premises exert important limitations on the applicability of the methods. And yet, high mountain sediment sources are rife with transient processes, such as non-steady erosion by glacial quarrying and/or landsliding, or temporary cosmic-ray shielding beneath glaciers and/or sediment. As well as breaching the premises of existing burial dating methods, such processes yield samples with low nuclide abundances and variable 26Al/10Be ratios that may foil both isochron and simple burial-age solutions. P–PINI (Particle-Pathway Inversion of Nuclide Inventories) is a new dating tool designed for dating the burial of sediments sourced from landscapes characterized by abrupt, non-steady erosion, discontinuous exposure, and catchments with elevation-dependent 26Al/10Be production ratios. P–PINI merges a Monte Carlo simulator with established cosmogenic nuclide production equations to simulate millions of samples (10Be–26Al inventories). The simulated samples are compared statistically with 10Be–26Al measured in field samples to define the most probable burial age. Here, we target three published 10Be–26Al datasets to demonstrate the versatility of the P–PINI model for dating fluvial and glacial sediments. (1) The first case serves as a robust validation of P–PINI. For the Pulu fluvial gravels (China), we obtain a burial age of 1.27 ± 0.10 Ma (1σ), which accords with the isochron burial age and two independent chronometers reported in Zhao et al. (2016) Quaternary Geochronology 34, 75–80. The second and third cases, however, reveal marked divergence between P–PINI and isochron-derived ages. (2) For the fluvial Nenana Gravel (USA), we obtain a minimum-limiting burial age of 4.5 ± 0.7 Ma (1σ), which is compatible with unroofing of the Alaska Range starting ∼ 6 Ma, while calling into question the Early Pleistocene isochron burial age presented in Sortor et al. (2021) Geology 49, 1473–1477. (3) For the Bünten Till (Switzerland), we obtain a limiting burial age of <204 ka (95th percentile range), which conforms with the classical notion of the most extensive glaciation in the northern Alpine Foreland assigned to the Riss glaciation (sensu marine isotope stage 6) contrary to the isochron burial age presented in Dieleman et al. (2022) Geosciences, 12, 39. Discrepancies between P–PINI and the isochron ages are rooted in the challenges posed by the diverse pre-burial 26Al/10Be ratios produced under conditions characteristic of high mountain landscapes; i.e., non-steady erosion, discontinuous cosmic-ray exposure, and elevation-dependent 26Al/10Be production ratios in the source region, which are incompatible with the isochron method, but easily accommodated by the stochastic design of P–PINI. 相似文献
342.
A new analytical method was evaluated for predicting scour profile downstream of a submerged sluice gate with an apron. The differential equations between bed Shear stress and Scour profile Curvature(SSC model) were utilized to predict the scour profile in both temporal and equilibrium stages. A jet momentum flux was considered as an external source of erosion on a hypothetical particle ring as the boundary between the flow and sediment bed. The scour length and sediment resistance factor were t... 相似文献
343.
A spatially averaged numerical model was developed to describe the erosion of cohesive sediment. Together with known empirical relations, the model comprises a new formulation for resuspension due to fish activity. Experiments on erosion of natural sediments in the annular flume at Aachen University are used for model calibration. Empirical coefficients were evaluated with genetic algorithms to achieve the best agreement between the model results and the experimental data. The presented model shows sufficient flexibility to account for various sediment properties, including different sediment sources, natural and artificial contaminants, presence or absence of aquatic organisms, and results in an average coefficient of determination, R2 = 90.5% between the model results and the experimental data. Model validation allows it to be assumed that different contaminants affect bed properties differently. Fish activity plays an essential role in correct resuspension prediction. Further sediment erosion experiments with carefully chosen conditions will allow a more comprehensive model evaluation. The presented model is intended to serve as a building block in the development of a hydraulic-sediment-biota model within the W3-Hydro: Water Quality Event Detection for Urban Water Security and Urban Water Management Based on Hydrotoxicological Investigations project that aims to improve the knowledge concerning bioavailability, transport, fate, and effects of contaminants on the aquatic environment. 相似文献
344.
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346.
Dávid Karátson Jean-Claude Thouret Ichio Moriya Alejandro Lomoschitz 《Bulletin of Volcanology》1999,61(3):174-193
The origin and development of erosion-modified, erosion-transformed, and erosion-induced depressions in volcanic terrains
are reviewed and systematized. A proposed classification, addressing terminology issues, considers structural, geomorphic,
and climatic factors that contribute to the topographic modification of summit or flank depressions on volcanoes. Breaching
of a closed crater or caldera generated by volcanic or non-volcanic processes results in an outlet valley. Under climates
with up to ∼2000–2500 mm annual rainfall, craters, and calderas are commonly drained by a single outlet. The outlet valley
can maintain its dominant downcutting position because it quickly enlarges its drainage basin by capturing the area of the
primary depression. Multi-drained volcanic depressions can form if special factors, e.g., high-rate geological processes,
such as faulting or glaciation, suppress fluvial erosion. Normal (fluvial) erosion-modified volcanic depressions the circular
rim of which is derived from the original rim are termed erosion craters or erosion calderas, depending on the pre-existing
depression. The resulting landform should be classed as an erosion-induced volcanic depression if the degradation of a cluster
of craters produces a single-drained, irregular-shaped basin, or if flank erosion results in a quasi-closed depression. Under
humid climates, craters and calderas degrade at a faster rate. Mostly at subtropical and tropical ocean-island and island-arc
volcanoes, their erosion results in so-called amphitheater valleys that develop under heavy rainfall (>∼2500 mm/year), rainstorms,
and high-elevation differences. Structural and lithological control, and groundwater in ocean islands, may in turn preform
and guide development of high-energy valleys through rockfalls, landsliding, mudflows, and mass wasting. Given the intense
erosion, amphitheater valleys are able to breach a primary depression from several directions and degrade the summit region
at a high rate. Occasionally, amphitheater valleys may create summit depressions without a pre-existing crater or caldera.
The resulting, negative landforms, which may drain in several directions and the primary origin of which is commonly unrecognizable,
should be included in erosion-transformed volcanic depressions.
Received: 4 January 1998 / Accepted: 18 January 1999 相似文献
347.
A two-phase numerical model for sediment transport prediction under oscillatory sheet flows 总被引:1,自引:0,他引:1
To predict sediment transport under oscillatory sheet flow condition, especially for fine sand, is still a challenging research subject in coastal engineering. This paper describes a newly-developed numerical model based on two-phase theory with the use of a one-equation turbulence closure, and its applications in predicting fine sediment suspension in near-prototype oscillatory sheet flow conditions. Model results were compared with comprehensive laboratory measurements of flow velocity and sediment concentration under both symmetrical and asymmetrical oscillatory sheet flows from a large-scale water tunnel. Good agreements between the model results and measurements were achieved and the results demonstrated that the model is capable of reproducing detailed characteristics of sediment entrainment process in the sheet flow regime. The comparisons also revealed the fact that the concentration peaks at flow reversal is associated with the strong vertical sediment transport flux in the pickup layer, which has been widely observed in many laboratory experiments. The effects of flow reversal events on total sediment transport were also discussed. 相似文献
348.
Yan LU Yongjun LU Xingnong ZHANG 《国际泥沙研究》2007,22(4):282-291
The stability of riverbanks subject to seepage is studied experimentally and theoretically in this paper. By including seepage in a 3-dimensional theoretical analysis, the study first shows how the critical slope or angle of repose of a cohesionless material is related to the ratio of the hydraulic gradient of seepage to its critical value under the fluidization condition. The critical stable slope is shown to be related to not only the hydraulic gradient but also the seepage direction. Measured laboratory data reasonably fit well with the theoretical relationship for the case of injection and suction. The data reveal that the slope is reduced with injection and increased with suction, respectively. Additionally, the study identifies the seepage direction which results in a minimum critical stable slope for a certain hydraulic gradient of seepage. 相似文献
349.
Previous quantitative studies of field-scale cyclic steps are mostly based on analysis of field data. Such studies have shed light on the erosion/deposition patterns over these morphological features as well as the magnitudes of the turbidity current parameters back estimated using the measured geometry data. However, it remains unclear to what extent such back estimated hydraulic features and erosion/deposition patterns can be numerically reproduced by process-based numerical models. Here, a tw... 相似文献
350.
针对唐岛湾内清淤工程,开展了唐岛湾整体动床物理模型试验。通过试验资料分析了在SW(西南)向极限波的作用下,波流动力调整以及湾内泥沙冲淤变化。试验表明,当水位高于平均高潮位时,方案一有效波高相对现状平均增大0.3m,方案二有效波高相对现状平均增大0.6m左右;工程区域内各测点的底流速变化基本上都具有周期性和非对称性,变化周期大约为10s,接近SW向入射波的波周期的2倍;方案二的动力环境与冲淤变化程度,好于方案一。试验研究成果可供类似工程应用时参考。 相似文献