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91.
A sedimentary sequence overlying a granite pluton near Ishkarwaz (upper Yarkhun valley, Chitral, Pakistan; Karakorum Microplate) contains abundant, but poorly preserved, acritarchs probably referable to the late early Arenig-early late Arenig interval. The palynological assemblages of Karakorum show a marked similarity to the cold water Peri-Gondwana assemblages; i.e. to those of Li Jun's Arbusculidium-Coryphidium-Striatotheca 'Mediterranean' Bioprovince. Biogeographical and geological comparisons suggest that, before the accretion of Cimmerian microplates to the Eurasian continent, the Karakorum Microplate was located along the northern margin of Gondwana in a latitude intermediate between the Mediterranean region and South China (Yangtze Platform). 相似文献
92.
Giorgio Rivalenti Maurizio Mazzucchelli Vicente Antonio Vitorio Girardi Giancarlo Cavazzini Cristina Finatti Maria Adelaide Barbieri Wilson Teixeira 《Lithos》1998,43(4):235-265
Paleoproterozoic basaltic, andesitic and rhyolitic dykes crosscut the Archaean Carajás basement. Basalts are distinguished into a high and a low TiO2 group (HTi and LTi), each group consisting of geochemically distinct NE- and NW-trending swarms. The HTi dykes are evolved transitional basalts having essentially EMORB-type geochemistry. The LTi basalts are tholeiites (NE-trending swarm) and high-Al basalts (NW-trending swarm) displaying incompatible trace elements patterns with variably negative Nb anomaly, enrichment in Rb, Ba, K (LILE) and La, Ce and Nd (LREE) and positive Sr anomaly. With respect to orogenic analogues, andesites have lower Al2O3, CaO and Ni, higher FeO, LILE, LREE, Nb, Zr and Ti and negative Sr anomaly. Rhyolites have geochemical characteristics comparable with those of A-type granites. At 1.8 Ga,
ranges from 0.700 to 0.705 in the HTi basalts and from 0.700 to 0.704 in the LTi group. Andesites define an isochron of 1874±110 Ma (Sro=0.7038±0.0010). Rhyolites from Southern and Northern Carajás define two isochrons of 1802±130 Ma (Sro=0.7062±0.0046) and 1535±82 Ga (Sro=0.7625) respectively, the younger date being interpreted as resetting of the Rb–Sr isotopic system. We propose a petrogenetic model relating LTi basalts with melting of lithospheric mantle metasomatized by acid melts derived from incipient melting of eclogites, representing in turn the subsolidus product of basaltic batches trapped in the mantle. The HTi basalts are explained by melting of the lithospheric mantle containing the complementary residual eclogite. Andesite petrogenesis is consistent with crystal fractionation from a high-Mg andesite parent derived from a mantle source more extensively metasomatized by eclogite-derived melts. Rhyolite composition is consistent with low melting degree of the basement rocks. The basalt–andesite–rhyolite dykes may represent the effects of crustal extension and arching in Carajás, which produced the anorogenic acid to intermediate magmatism (Uatumã group) and affecting a large part of the Amazon craton between 1.85 and 1.7 Ga. 相似文献
93.
Wavelet analysis for the regional-residual and local separation of potential field anomalies 总被引:1,自引:0,他引:1
A method based on the discrete wavelet transform was applied to the regional-residual separation of potential fields and to the filtering of local anomalies. A specific space-scale wavelet analysis, called multiresolution analysis, allowed decomposition of the signal with respect to a vast range of scales. Different analysing wavelets were applied to anomalies in both synthetic and real cases, but the more appropriate basis needed to be chosen by requiring the maximum compactness for the multiresolution analysis. Moreover, since such analysis was found not to be shift-invariant, the same criterion was applied to choosing the best signal shift. Application of the technique to both synthetic and real cases produced an optimal space-scale representation of the fields and a consistent regional-residual separation. Furthermore, the space localization allowed a variety of filtered signals to be obtained, each one with a specific scale and local area content. Fourier and wavelet analyses were both applied to the filtering out of the intense Etna anomaly from the aeromagnetic field of Sicily. The wavelet method was more powerful, suppressing only the Etna volcano anomaly and leaving the rest of the map practically unchanged. 相似文献
94.
The distribution of element abundances with redshift in Damped Lyα (DLA) systems can be adequately reproduced by the same
models reproducing the halo and disk components of the Milky Way Galaxy at different galactocentric distances. In this sense,
DLA systems are well represented by normal spiral galaxies in their early evolutionary stages.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
95.
Maurizio Ternullo 《Solar physics》1987,112(1):143-151
This work is a study of the rotational properties of the solar calcium plages, during the time interval 1967–1977; only plages older than 4 days have been the object of this research. We have looked systematically for any significant change occurring during the course of the solar cycle, and any kind of ‘anomaly’ or fine structure in the differential rotation latitudinal profile. We find that such a profile undergoes a cyclic transformation, making it assume the highest steepness at the solar maximum; a sudden flattening then occurs in the first years of declining activity; the last years of the cycle, as the first years of the next one, are characterized by intermediate steepness values. Moreover, we find that, in spite of the general belief that the angular rotation rate is continuously decreasing with increasing heliographic latitude, at least two inversions do exist of such an overall tendency:
- A narrow, minimal angular-rotation-rate strip lies very close to the equatorward margin of the plage production band; this feature shifts continuously, in a wave-like manner, throughout the solar cycle, from 15/18° to 3/6° latitude.
- A narrow, maximal angular-rotation-rate strip has been observed lying in the neighbourhood of the poleward margin of the activity band; a process of continuous transformation of the rotation rate profile is always active, in a narrow latitude strip on the equatorward side of such a feature, generating new features of the same kind, which replace the older ones, that disappeared due to the equatorward shift of the plage zone. All that simulates an equatorward shift of the observed ‘anomalies’; we observed them until the minimum activity epoch (1976), at 15/18° latitude. Some relations of these features with both torsionai waves (Howard and LaBonte, 1980) and magnetic activity are briefly discussed.
96.
We formulate a two-stage scheme for astrophysical turbulence in the frame of a revised Kolmogorov self-similar theory, hierarchical in nature. According to this approach, graviaation is revealed to be the main source of dissipated energy supporting the turbulent cascade. Results are compared with observational data about molecular clouds in the Galaxy and with the forecastings of an intermittent model of the same authors. 相似文献
97.
Giorgio?RivalentiEmail author Alberto?Zanetti Maurizio?Mazzucchelli Riccardo?Vannucci Carlos?A.?Cingolani 《Contributions to Mineralogy and Petrology》2004,147(6):647-670
Amphibole ± phlogopite ± apatite-bearing mantle xenoliths at Gobernador Gregores display modal, bulk-rock and phase geochemical characteristics held as indicators of carbonatitic metasomatism. However, part of these xenoliths has high TiO2/Al2O3 and those displaying the most pronounced carbonatitic geochemical markers modally trend towards harzburgite. Bulk-rock, clinopyroxene and amphibole show Zr, Hf and Ti negative anomalies, which increase at decreasing Na2O and high field strength elements (HFSE) concentrations. Steady variation trends between xenoliths which have and do not have carbonatitic characteristics suggest a control by reactive porous flow of only one agent, inferred to be initially a ne-normative hydrous basalt (because of the presence of wehrlites) evolving towards silica saturation. Variation trends exhibit cusps when amphibole appears in the mode. Appearance of amphibole may explain the Ti anomaly variations, but not those of Zr and Hf. Numerical modelling [Plate Model (Vernières et al. in J Geophys Res 102:24771–24784, 1997)] gives results consistent with the observed geochemical features by assuming the presence of loveringite. Modest HFSE anomalies in the infiltrating melt may be acquired during percolation in the garnet-facies.In memory of Carlo Rivalenti 相似文献
98.
Maurizio Righetti 《Acta Geophysica》2008,56(3):801-823
The paper addresses the problem of the resistance due to vegetation in an open channel flow, characterized by partially and
fully submerged vegetation formed by colonies of bushes. The flow is characterized by significant spatial variations of velocity
between vertical profiles that make the traditional approach based on time averaging of turbulent fluctuations inconvenient.
A more useful procedure, based on time and spatial averaging (Double-Averaging Method) is applied for the flow field analysis
and characterization. The vertical distribution of mean velocity and turbulent stresses at different spatial locations has
been measured with a 3D Acoustic Doppler Velocimeter (ADV) for two different vegetation densities where fully submerged real
bushes (salix pentandra) have been used. Velocity measurements were completed together with the measurements of drag exerted
on the flow by bushes at different flow depths. The analysis of velocity measurements allows depicting the fundamental characteristics
of both the mean flow field and turbulence. The experimental data show that the contribution of form-induced stresses to the
momentum balance cannot be neglected. The mean velocity profiles and the spatially averaged turbulent intensity profiles allow
inferring that the vegetation density is a driving parameter for the development of a mixing layer at the canopy top in the
case of submerged vegetation. Moreover, the net upward turbulent momentum flux, evaluated with the methodology proposed by
Lu and Willmarth (1973), appears to be damped for increased vegetation density; this finding can rationally explain the reduction
of the suspended sediment transport capacity typically observed in free surface flows over a vegetated bed. 相似文献
99.
Linah Mohamed Ben Calderhead Maurizio Filippone Mike Christie Mark Girolami 《Computational Geosciences》2012,16(2):423-436
This paper presents the application of a population Markov Chain Monte Carlo (MCMC) technique to generate history-matched
models. The technique has been developed and successfully adopted in challenging domains such as computational biology but
has not yet seen application in reservoir modelling. In population MCMC, multiple Markov chains are run on a set of response
surfaces that form a bridge from the prior to posterior. These response surfaces are formed from the product of the prior
with the likelihood raised to a varying power less than one. The chains exchange positions, with the probability of a swap
being governed by a standard Metropolis accept/reject step, which allows for large steps to be taken with high probability.
We show results of Population MCMC on the IC Fault Model—a simple three-parameter model that is known to have a highly irregular
misfit surface and hence be difficult to match. Our results show that population MCMC is able to generate samples from the
complex, multi-modal posterior probability distribution of the IC Fault model very effectively. By comparison, previous results
from stochastic sampling algorithms often focus on only part of the region of high posterior probability depending on algorithm
settings and starting points. 相似文献
100.
Andrea Bollati Sveva Corrado Maurizio Marino 《International Journal of Earth Sciences》2012,101(4):1011-1031
The western Lucretili Mts. in the central Apennines (Latium, Italy) have been recently re-mapped in great detail and are the subject of combined stratigraphic, sedimentological and structural investigations. In this paper, we present a new stratigraphic interpretation of the Jurassic paleogeography of western Lucretili Mts., where a rift-derived intrabasinal paleo-high of the Alpine Tethys has been identified for the first time by means of facies analysis and biostratigraphic dating. Recognised facies associations, combined with dated stratigraphic sections, allow to define the morphology of the structural paleo-high and to identify the associated gravity-driven deposits (olistoliths) accumulated in the surrounding basin. Furthermore, we investigated the modes of interaction between Jurassic extensional structures and the subsequent contractional patterns developed during the Tertiary mountain building. In detail, the role played during Apennines tectonics by the paleo-escarpments bounding the paleo-high and by the surrounding olistoliths has been analysed. The paleo-escarpments either acted as focussing features for ENE-directed frontal thrust ramp localisation and were offset with small shortening amounts or reactivated as NNE striking high angle transpressional faults or preserved the original geometries as a result of variable orientation of paleo-escarpments with respect to the Neogene compressive stress field (with ENE oriented sigma1). Newly formed ENE striking tear faults connect these either inherited or neo-formed discontinuities. This complex stratigraphic and structural pattern is substantially different from the previous interpretations of this portion of the central Apennines based on a hypothesised layer-cake stratigraphy deformed by neo-formed Neogene thrusts. This contribution strengthens the importance of integrating facies analyses and structural investigations to detect the influence of pre-orogenic structures on compressive structural patterns, in an area where commercial seismic lines are not available and cannot help in reconstructing the subsurface geometries. 相似文献