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251.
Journal of Earth System Science - Hydrological models are simplified representations of natural processes and subject to errors. Uncertainty bounds are a commonly used way to assess the impact of... 相似文献
252.
Time-scales of recent Phlegrean Fields eruptions inferred from the application of a ‘diffusive fractionation’ model of trace elements 总被引:2,自引:1,他引:1
Diego Perugini Giampiero Poli Maurizio Petrelli Cristina P. De Campos D. B. Dingwell 《Bulletin of Volcanology》2010,72(4):431-447
The variation of chemical element compositions in two pyroclastic sequences (Astroni 6 and Averno 2, Phlegrean Fields, Italy)
is studied. Both sequences are compositionally zoned indicating a variability of melt compositions in the magma chamber prior
to eruption. A clear dichotomy between the behaviour of major vs. trace elements is also observed in both sequences, with
major elements displaying nearly linear inter-elemental trends and trace elements showing a variable scattered behaviour.
Together with previous petrological investigations these observations are consistent with the hypothesis that magma mixing
processes played a key role in the evolution of these two magmatic systems. Recently it has been suggested that mixing processes
in igneous systems may strongly influence the mobility of trace elements inducing a ‘diffusive fractionation’ phenomenon,
whose extent depends on the mixing time-scale. Here we merge information from 1) numerical simulations of magma mixing, and
2) magma mixing experiments (using as end-members natural compositions from Phlegrean Fields) to derive a relationship relating
the degree of ‘diffusive fractionation’ to the mixing time-scales. Application of the ‘diffusive fractionation’ model to the
two studied pyroclastic sequences allowed us to apply the relationship derived by numerical simulations and experiments to
estimate the mixing time-scales for these two magmatic systems. Results indicate that mixing processes in Astroni 6 and Averno
2 systems lasted for approximately 2 and 9 days, respectively, prior to eruption. 相似文献
253.
Jonathan J. Sparks Diego Janches Michael J. Nicolls Craig Heinselman 《Journal of Atmospheric and Solar》2010,72(16):1221-1230
Over the past decade, High Power and Large Aperture (HPLA) radars have been widely utilized for the study of sub-millimeter extraterrestrial particles via the detection of the meteor head-echo. These observations have been a successful tool in the study of the sporadic meteor background, however, they have been limited by the lack of precise knowledge of the particle's location within the radar beam and its absolute trajectory and velocity. This limitation prevents for example the accurate determination of the meteors radiant and orbit. Interferometry measurements of the head-echo has been proven to be a detection technique that satisfies this need. Unfortunately very few radars are capable of performing them. We have developed a methodology which takes advantage of the multi-receiving capabilities of the 450 MHz Poker Flat Incoherent Scatter Radar (PFISR) enabling us to utilize the phased array of crossed-dipoles as an interferometer. This new PFISR capability allows us to determine the instantaneous position of meteors within the radar beam. This enables us to determine absolute velocities and ultimately meteor radiant and orbit around the Sun. In this work, we present initial results from 9 h of observations during which 142 particles were individually detected by the three different receiving channels simultaneously. For these meteors absolute velocities were obtained and meteor dynamical, physical and radiant properties were derived. 相似文献
254.
255.
We study the peculiar velocity field inferred from the Mark III spirals using a new method of analysis. We estimate optimal values of Tully–Fisher scatter and zero-point offset, and we derive the three-dimensional rms peculiar velocity ( σ v ) of the galaxies in the samples analysed. We check our statistical analysis using mock catalogues derived from numerical simulations of cold dark matter (CDM) models considering measurement uncertainties and sampling variations. Our best determination for the observations is σ v =(660±50) km s−1 . We use the linear theory relation between σ v , the density parameter Ω, and the galaxy correlation function ξ ( r ) to infer the quantity , where b is the linear bias parameter of optical galaxies and the uncertainties correspond to bootstrap resampling and an estimated cosmic variance added in quadrature. Our findings are consistent with the results of cluster abundances and redshift-space distortion of the two-point correlation function. These statistical measurements suggest a low value of the density parameter Ω∼0.4 if optical galaxies are not strongly biased tracers of mass. 相似文献
256.
Gustavo E. Romero † Diego F. Torres I. Andruchow Luis A. Anchordoqui Bennett Link † 《Monthly notices of the Royal Astronomical Society》1999,308(3):799-806
Based on Link & Epstein's study of temporal asymmetry of 631 gamma-ray bursts from the BATSE 3B catalogue, we identify the population of bursts with rising times that are longer than their decays, thus showing atypical profiles. We analyse their sky distribution, morphology, time–space clustering and other average properties and compare them with those associated with the bulk of the bursts. We show how most of the peculiar bursts analysed are consistent with recent fireball models, but a fraction of bursts (∼4 per cent of the total sample) appear to be inconsistent. 相似文献
257.
Diego Barba Claude Robin Pablo Samaniego Jean-Philippe Eissen 《Journal of Volcanology and Geothermal Research》2008
Ice-capped Chimborazo is one of the large composite Ecuadorian volcanoes whose recent eruptive activity is poorly known. This paper presents the characteristics and the ages of a newly discovered Holocene sequence of pyroclastic deposits on the east and north sides of the cone. Lying upon a moraine of the Late-Glacial period, the most complete section of ~ 4.5 m in thickness is located 5 km from the present summit crater. It consists of seven massive or diffusely stratified ash flow layers and four fallout layers interbedded with seven paleosoils. 相似文献
258.
Laura Serra Marc Saez Pablo Juan Diego Varga Jorge Mateu 《Stochastic Environmental Research and Risk Assessment (SERRA)》2014,28(7):1671-1684
Wildfires have been studied in many ways, for instance as a spatial point pattern or through modeling the size of fires or the relative risk of big fires. Lately a large variety of complex statistical models can be fitted routinely to complex data sets, in particular wildfires, as a result of widely accessible high-level statistical software, such as R. The objective in this paper is to model the occurrence of big wildfires (greater than a given extension of hectares) using an adapted two-part econometric model, specifically a hurdle model. The methodology used in this paper is useful to determine those factors that help any fire to become a big wildfire. Our proposal and methodology can be routinely used to contribute to the management of big wildfires. 相似文献
259.
Doriam Restrepo Juan David Gómez Juan Diego Jaramillo 《Pure and Applied Geophysics》2014,171(9):2185-2198
We present a closed-form frequency-wave number (ω – k) Green’s function for a layered, elastic half-space under SH wave propagation. It is shown that for every (ω – k) pair, the fundamental solution exhibits two distinctive features: (1) the original layered system can be reduced to a system composed by the uppermost superficial layer over an equivalent half-space; (2) the fundamental solution can be partitioned into three different fundamental solutions, each one carrying out a different physical interpretation, i.e., an equivalent half-space, source image impact, and dispersive wave effect, respectively. Such an interpretation allows the proper use of analytical and numerical integration schemes, and ensures the correct assessment of Cauchy principal value integrals. Our method is based upon a stiffness-matrix scheme, and as a first approach we assume that observation points and the impulsive SH line-source are spatially located within the uppermost superficial layer. We use a discrete wave number boundary element strategy to test the benefits of our fundamental solution. We benchmark our results against reported solutions for an infinitely long circular canyon subjected to oblique incident SH waves within a homogeneous half-space. Our results show an almost exact agreement with previous studies. We further shed light on the impact of horizontal strata by examining the dynamic response of the circular canyon to oblique incident SH waves under different layered half-space configurations and incident angles. Our results show that modifications in the layering structure manifest by larger peak ground responses, and stronger spatial variability due to interactions of the canyon geometry with trapped Love waves in combination with impedance contrast effects. 相似文献
260.
Modeling the effects of pulsed versus chronic sand inputs on salmonid spawning habitat in a low‐gradient gravel‐bed river
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Oscar Maturana Daniele Tonina James A. McKean John M. Buffington Charles H. Luce Diego Caamaño 《地球表面变化过程与地形》2014,39(7):877-889
It is widely recognized that high supplies of fine sediment, largely sand, can negatively impact the aquatic habitat quality of gravel‐bed rivers, but effects of the style of input (chronic vs. pulsed) have not been examined quantitatively. We hypothesize that a continuous (i.e. chronic) supply of sand will be more detrimental to the quality of aquatic habitat than an instantaneous sand pulse equal to the integrated volume of the chronic supply. We investigate this issue by applying a two‐dimensional numerical model to a 1 km long reach of prime salmonid spawning habitat in central Idaho. Results show that in both supply scenarios, sand moves through the study reach as bed load, and that both the movement and depth of sand on the streambed mirrors the hydrograph of this snowmelt‐dominated river. Predictions indicate greater and more persistent mortality of salmonid embryos under chronic supplies than pulse inputs, supporting our hypothesis. However, predicted mortality varies both with salmonid species and location of spawning. We found that the greatest impacts occur closer to the location of the sand input under both supply scenarios. Results also suggest that reach‐scale morphology may modulate the impact of sand loads, and that under conditions of high sand loading climate‐related increases in flow magnitude could increase embryo mortality through sand deposition, rather than streambed scour. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献