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171.
Sebastián Tomás Sánchez Gómez Jens Ormö Carl Alwmark Sanna Holm-Alwmark Gabriel Zachén Robert Lilljequist Juan Antonio Sánchez Garrido 《Meteoritics & planetary science》2023,58(10):1512-1539
The Tabernas–Alhabia Basin is a structural depression situated in the province of Almería, southeastern Spain. The basin is filled with Neogene, Pliocene, and Pleistocene sediments resting discordantly on a Paleozoic metamorphic basement. During the marine Tortonian sedimentation, a bed of breccia (Gordo megabed) was formed. It consists of rotated sedimentary megablocks commonly capped and/or surrounded by a polymict breccia composed mainly of up to dm-sized clasts of the crystalline (schist) basement. Previous work has suggested the bed to be a seismite corresponding to events induced by earthquakes. Here, we link the formation of the Gordo megabed with an ∼5 km wide, rimmed depression with exposed breccias on the northern flank of the Sierra de Gádor mountain. This semicircular structure, developed in mainly schists and dolostone of the basement, is delimited to the W, S, and E by an up to 350 m high escarpment with overturned stratigraphy. Toward the north, this crater-like structure opens toward the Gordo megabed of the Tabernas Basin. In the southern sector, the overturned strata transform outward for into a blocky allochthonous breccia with decreasing thickness and clast size. In the interior of the structure, there are occurrences of graded breccia and arenite superposed on a blocky, autochthonous breccia. Based on the presence of mineralogical shock metamorphic evidence, potential shatter cones, and a high Ir anomaly (∼500 ppb) as well as the position of the structure near the town of Alhama de Almería, we propose to call it the Alhama de Almería impact structure. 相似文献
172.
Lucia Villar-Muñoz Jan H. Behrmann Juan Diaz-Naveas Dirk Klaeschen Jens Karstens 《Geo-Marine Letters》2014,34(2-3):185-198
Between 33°S and 47°S, the southern Chile forearc is affected by the subduction of the aseismic Juan Fernandez Ridge, several major oceanic fracture zones on the subducting Nazca Plate, the active Chile Ridge spreading centre, and the underthrusting Antarctic Plate. The heat flow through the forearc was estimated using the depth of the bottom simulating reflector obtained from a comprehensive database of reflection seismic profiles. On the upper and middle continental slope along the whole forearc, heat flow is about 30–60 mW m–2, a range of values common for the continental basement and overlying slope sediments. The actively deforming accretionary wedge on the lower slope, however, in places shows heat flow reaching about 90 mW m–2. This indicates that advecting pore fluids from deeper in the subduction zone may transport a substantial part of the heat there. The large size of the anomalies suggests that fluid advection and outflow at the seafloor is overall diffuse, rather than being restricted to individual fault structures or mud volcanoes and mud mounds. One large area with very high heat flow is associated with a major tectonic feature. Thus, above the subducting Chile Ridge at 46°S, values of up to 280 mW m–2 indicate that the overriding South American Plate is effectively heated by subjacent zero-age oceanic plate material. 相似文献
173.
Crawford et al. (Boundary-Layer Meteorol 66:237–245, 1993) showed that the time average is inappropriate for airborne eddy-covariance flux calculations. The aircraft’s ground speed through a turbulent field is not constant. One reason can be a correlation with vertical air motion, so that some types of structures are sampled more densely than others. To avoid this, the time-sampled data are adjusted for the varying ground speed so that the modified estimates are equivalent to spatially-sampled data. A comparison of sensible heat-flux calculations using temporal and spatial averaging methods is presented and discussed. Data of the airborne measurement systems $\hbox {M}^2\hbox {AV}$ , Helipod and Dornier 128-6 are used for the analysis. These systems vary in size, weight and aerodynamic characteristics, since the $\hbox {M}^2\hbox {AV}$ is a small unmanned aerial vehicle (UAV), the Helipod a helicopter-borne turbulence probe and the Dornier 128-6 a manned research aircraft. The systematic bias anticipated in covariance computations due to speed variations was neither found when averaging over Dornier, Helipod nor UAV flight legs. However, the random differences between spatial and temporal averaging fluxes were found to be up to 30 % on the individual flight legs. 相似文献
174.
Changes in the oceanic current system and in the oceanic mass distribution alter, together with other processes, the state
of the Earth’s rotation. This state is characterized by the length of day (LOD) and the tilt of the pole-to-pole axis. The
aim of our study was to derive the respective governing physical mechanisms in the ocean. Therefore, Earth rotation observations
were assimilated into a global circulation model of the ocean. Although assimilation is a well-established tool in climate
science, the assimilation of Earth rotation observations into a global ocean model was done here for the first time. Prior
to the assimilation, the Earth rotation observations were projected onto the angular momentum of the ocean. Non-oceanic contributions
were removed. The result of the subsequent assimilation procedure is a time varying ocean model state that reproduces the
projected Earth rotation observations well. This solution was studied to understand the oceanic generation of Earth rotation
deviations and to identify governing physical mechanisms. This paper focuses on LOD anomalies although polar motion was assimilated
simultaneously. Our results indicate that changes in the oceanic LOD excitation are mostly attributed to changes in total
ocean mass. Changes in the spatial distribution of ocean mass turned out to have a minor contribution to the LOD deviations.
The same applies to changes in the current system. 相似文献
175.
Jens R?der Raimon Tolosana-Delgado Fred A. Hamprecht 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(7):865-879
The aim of this paper is to compare four different methods for binary classification with an underlying Gaussian process with
respect to theoretical consistency and practical performance. Two of the inference schemes, namely classical indicator kriging
and simplicial indicator kriging, are analytically tractable and fast. However, these methods rely on simplifying assumptions
which are inappropriate for categorical class labels. A consistent and previously described model extension involves a doubly
stochastic process. There, the unknown posterior class probability f(·) is considered a realization of a spatially correlated Gaussian process that has been squashed to the unit interval, and
a label at position x is considered an independent Bernoulli realization with success parameter f(x). Unfortunately, inference for this model is not known to be analytically tractable. In this paper, we propose two new computational
schemes for the inference in this doubly stochastic model, namely the “Aitchison Maximum Posterior” and the “Doubly Stochastic
Gaussian Quadrature”. Both methods are analytical up to a final step where optimization or integration must be carried out
numerically. For the comparison of practical performance, the methods are applied to storm forecasts for the Spanish coast
based on wave heights in the Mediterranean Sea. While the error rate of the doubly stochastic models is slightly lower, their
computational cost is much higher. 相似文献
176.
Lutz Nasdala Dieter Grambole Jens Götze Ulf Kempe Tamás Váczi 《Contributions to Mineralogy and Petrology》2011,161(5):777-789
Synthetic ZrSiO4 and (mildly to strongly radiation-damaged) natural zircon samples were irradiated with 8.8 MeV 4He2+ ions (fluences in the range 1 × 1013–5 × 1016 ions/cm2). For comparison, an additional irradiation experiment was done with 30 MeV 16O6+ ions (fluence 1 × 1015 ions/cm2). The light-ion irradiation resulted in the generation of new (synthetic ZrSiO4) or additional (mildly to strongly metamict natural samples) damage. The maximum extent of the damage is observed in a shallow
depth range approximately 32–33 μm (8.8 MeV He) and ~12 μm (30 MeV O) below the sample surface, i.e. near the end of the ion
trajectories. These depth values, and the observed damage distribution, correspond well to defect distribution patterns as
predicted by Monte Carlo simulations. The irradiation damage is recognised from the notable broadening of Raman-active vibrational
modes, lowered interference colours (i.e. decreased birefringence), and changes in the optical activity (i.e. luminescence
emission). At very low damage levels, a broad-band yellow emission centre is generated whereas at elevated damage levels,
this centre is suppressed and samples experience a general decrease in their emission intensity. Most remarkably, there is
no indication of notable structural recovery in pre-damaged natural zircon as induced by the light-ion irradiation, which
questions the relevance of alpha-assisted annealing of radiation damage in natural zircon. 相似文献
177.
Continental slope terraces at the southern Argentine margin are part of a significant contourite depositional system composed of a variety of drifts, channels, and sediment waves. Here, a refined seismostratigraphic model for the sedimentary development of the Valentin Feilberg Terrace located in ~4.1?km water depth is presented. Analyzing multichannel seismic profiles across and along this terrace, significant changes in terrace morphology and seismic reflection character are identified and interpreted to reflect variations in deep water hydrography from Late Miocene to recent times, involving variable flow of Antarctic Bottom Water and Circumpolar Deep Water. A prominent basin-wide aggradational seismic unit is interpreted to represent the Mid-Miocene climatic optimum (~17?C14?Ma). A major current reorganization can be inferred for the time ~14?C12?Ma when the Valentin Feilberg Terrace started growing due to the deposition of sheeted and mounded drifts. After ~12?Ma, bottom water flow remained vigorous at both margins of the terrace. Another intensification of bottom flow occurred at ~5?C6?Ma when a mounded drift, moats, and sediment waves developed on the terrace. This may have been caused by a general change in deep water mass organization following the closure of the Panamanian gateway, and a subsequent stronger southward flow of North Atlantic Deep Water. 相似文献
178.
Antonio Segalini Jens H. M. Fransson P. Henrik Alfredsson 《Boundary-Layer Meteorology》2013,148(2):269-283
An analysis of velocity statistics and spectra measured above a wind-tunnel forest model is reported. Several measurement stations downstream of the forest edge have been investigated and it is observed that, while the mean velocity profile adjusts quickly to the new canopy boundary condition, the turbulence lags behind and shows a continuous penetration towards the free stream along the canopy model. The statistical profiles illustrate this growth and do not collapse when plotted as a function of the vertical coordinate. However, when the statistics are plotted as function of the local mean velocity (normalized with a characteristic velocity scale), they do collapse, independently of the streamwise position and freestream velocity. A new scaling for the spectra of all three velocity components is proposed based on the velocity variance and integral time scale. This normalization improves the collapse of the spectra compared to existing scalings adopted in atmospheric measurements, and allows the determination of a universal function that provides the velocity spectrum. Furthermore, a comparison of the proposed scaling laws for two different canopy densities is shown, demonstrating that the vertical velocity variance is the most sensible statistical quantity to the characteristics of the canopy roughness. 相似文献
179.
Morten A. D. Larsen Peter Thejll Jens H. Christensen Jens C. Refsgaard Karsten H. Jensen 《Climate Dynamics》2013,40(11-12):2903-2918
We investigate the simulated temperature and precipitation of the HIRHAM regional climate model using systematic variations in domain size, resolution and detailed location in a total of eight simulations. HIRHAM was forced by ERA-Interim boundary data and the simulations focused on higher resolutions in the range of 5.5–12 km. HIRHAM outputs of seasonal precipitation and temperature were assessed by calculating distributed model errors against a higher resolution data set covering Denmark and a 0.25° resolution data set covering Europe. Furthermore the simulations were statistically tested against the Danish data set using bootstrap statistics. The results from the distributed validation of precipitation showed lower errors for the winter (DJF) season compared to the spring (MAM), fall (SON) and, in particular, summer (JJA) seasons for both validation data sets. For temperature, the pattern was in the opposite direction, with the lowest errors occurring for the JJA season. These seasonal patterns between precipitation and temperature are seen in the bootstrap analysis. It also showed that using a 4,000 × 2,800 km simulation with an 11 km resolution produced the highest significance levels. Also, the temperature errors were more highly significant than precipitation. In similarly sized domains, 12 of 16 combinations of variables, observation validation data and seasons showed better results for the highest resolution domain, but generally the most significant improvements were seen when varying the domain size. 相似文献
180.
Uta Fritze-von Alvensleben Peter Weilbacher Jens Bicker 《Astrophysics and Space Science》2003,284(2):893-896
To account for the range of stellar metallicities in local galaxies and for the increasing importance of low metallicities
at higher redshift we present chemically consistent models for the spectral and chemical evolution of galaxies over cosmological
timescales. We discuss advantages, limitations and future prospects of our approach.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献