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711.
The Bündnerschiefer of the Swiss-Italian Alps is a large sedimentary complex deposited on the Piemonte–Liguria and Valais oceans and associated continental margins from the upper Jurassic to Eocene. It is made of a large variety of sequences associated or not with an ophiolitic basement. The Bündnerschiefer makes an accretionary prism that developed syn-tectonically from the onset of alpine subduction, and it records orogenic metamorphism following episodes of HP metamorphism. The Bündnerschiefer shares important similarities with the Otago schists of New Zealand and with the Wepawaug schists of Connecticut, both of which form accretionary prisms and have an orogenic metamorphic imprint.With the aim of testing the hypothesis of mobility of chemical components as a function of metamorphic grade, in this work I present fifty-five bulk chemical analyses of various lithological facies of the Bündnerschiefer collected along the well-studied field gradient of the Lepontine dome of Central Switzerland, in the Prättigau half window of East Switzerland, and in the Tsaté Nappe of Valle d'Aosta (Italy). The dataset includes the concentration of major components, large ion lithophile elements (Rb, Sr, Ba, Cs), high field strength elements (Zr, Ti, Nb, Th, U, Ta, Hf), fluid-mobile light elements (B, Li), volatiles (CO2, S), REEs, and Y, V, Cr, Co, Sn, Pb, Cu, Zn, Tl, Sb, Be, and Au. These data are compared against the compositions of the global marine sediment reservoir, typical crustal reservoirs, and against the previously measured compositions of Otago and Wepawaug schists. Results reveal that, irrespective of their metamorphic evolution, the bulk chemical compositions of orogenic metasediments are characterized by mostly constant compositional ratios (e.g., K2O/Al2O3, Ba/Al2O3, Sr/CaO, etc.), whose values in most cases are undistinguishable from those of actual marine sediments and other crustal reservoirs. For these rocks, only volatile concentrations decrease dramatically as a function of metamorphic temperature, and significant deviations from the reservoir signatures are evident for SiO2, B, and Li. These results are interpreted as an indication of residual enrichment in the sediments, a process taking place during syn-metamorphic dehydration from the onset of metamorphism in a regime of chemical immobility. Residual enrichment increased the absolute concentrations of the chemical components of these rocks, but did not modify significantly their fundamental ratios. This poor compositional modification of the sediments indicates that orogenic metamorphism in general does not promote significant mass transfer from accretionary prisms. In contrast, mass transfer calculations carried out in a shear zone crosscutting the Bündnerschiefer shows that significant mass transfer occurs within these narrow zones, resulting in gains of H2O, SiO2, Al2O3, K2O, Ba, Y, Rb, Cu, V, Tl, Mo, and Ce during deformation and loss of Na2O, CO2, S, Ni, B, U, and Pb from the rock. These components were presumably transported by an aquo-carbonic fluid along the shear zone. These distinct attitudes to mobilize chemical elements from orogenic sediments may have implications for a potentially large number of geochemical processes in active continental margins, from the recycling of chemical components at plate margins to the genesis of hydrothermal ore deposits. 相似文献
712.
Stefania Bilardi Paolo S. Calabrò Sabine Caré Nicola Moraci Chicgoua Noubactep 《洁净——土壤、空气、水》2013,41(9):835-843
Current knowledge of the basic principles underlying the design of Fe0 beds is weak. The volumetric expansive nature of iron corrosion was identified as the major factor determining the sustainability of Fe0 beds. This work attempts to systematically verify developed concepts. Pumice and sand were admixed to 200 g of Fe0 in column studies (50:50 volumetric proportion). Reference systems containing 100% of each material have been also investigated. The mean grain size of the used materials (in mm) were 0.28 (sand), 0.30 (pumice), and 0.50 (Fe0). The five studied systems were characterized (i) by the time dependent evolution of their hydraulic conductivity (permeability) and (ii) for their efficiency for aqueous removal of CuII, NiII, and ZnII (about 0.3 mM of each). Results showed unequivocally that (i) quantitative contaminant removal was coupled to the presence of Fe0, (ii) additive admixture lengthened the service life of Fe0 beds, and (iii) pumice was the best admixing agent for sustaining permeability while the Fe0/sand column was the most efficient for contaminant removal. The evolution of the permeability was well‐fitted by the approach that the inflowing solution contained dissolved O2. The achieved results are regarded as starting point for a systematic research to optimize/support Fe0 filter design. 相似文献
713.
714.
The presence of scaling statistical properties in temporal rainfall has been well established in many empirical investigations during the latest decade. These properties have more and more come to be regarded as a fundamental feature of the rainfall process. How to best use the scaling properties for applied modelling remains to be assessed, however, particularly in the case of continuous rainfall time‐series. One therefore is forced to use conventional time‐series modelling, e.g. based on point process theory, which does not explicitly take scaling into account. In light of this, there is a need to investigate the degree to which point‐process models are able to ‘unintentionally’ reproduce the empirical scaling properties. In the present study, four 25‐year series of 20‐min rainfall intensities observed in Arno River basin, Italy, were investigated. A Neyman–Scott rectangular pulses (NSRP) model was fitted to these series, so enabling the generation of synthetic time‐series suitable for investigation. A multifractal scaling behaviour was found to characterize the raw data within a range of time‐scales between approximately 20 min and 1 week. The main features of this behaviour were surprisingly well reproduced in the simulated data, although some differences were observed, particularly at small scales below the typical duration of a rain cell. This suggests the possibility of a combined use of the NSRP model and a scaling approach, in order to extend the NSRP range of applicability for simulation purposes. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
715.
716.
717.
Stephen Serjeant † Alberto Carramiñana † Eduardo Gonzáles-Solares Phillipe Héraudeau Raúl Mújica † Ismael Perez-Fournon Nicola Sedgwick † Michael Rowan-Robinson Alberto Franceschini Thomas Babbedge Carlos del Burgo Paolo Ciliegi reas Efstathiou Fabio La Franca Carlotta Gruppioni David Hughes Carlo Lari Seb Oliver Francesca Pozzi Manfred Stickel Mattia Vaccari 《Monthly notices of the Royal Astronomical Society》2004,355(3):813-818
718.
Andrea Tiengo Paolo Esposito Sandro Mereghetti Lara Sidoli Diego Götz Marco Feroci Roberto Turolla Silvia Zane Gian Luca Israel Luigi Stella Peter Woods 《Astrophysics and Space Science》2007,308(1-4):33-37
We present a systematic analysis of all the BeppoSAX data of SGR1900+14. The observations spanning five years show that the source was brighter than usual on two occasions: ~20 days after the August 1998 giant flare and during the 105?s long X-ray afterglow following the April 2001 intermediate flare. In the latter case, we explore the possibility of describing the observed short term spectral evolution only with a change of the temperature of the blackbody component. In the only BeppoSAX observation performed before the giant flare, the spectrum of the SGR1900+14 persistent emission was significantly harder and detected also above 10 keV with the PDS instrument. In the last BeppoSAX observation (April 2002) the flux was at least a factor 1.2 below the historical level, suggesting that the source was entering a quiescent period. 相似文献
719.
Open-shutter RHESSI observations of 3–15 keV X-rays are found to exhibit active-region transient brightenings and microflares
at a rate of a least 10 per hour occurring even during the periods of lowest solar activity so far in the mission. A thermal
component fitted by temperatures of 6–14 MK dominates from 3 keV to about 9 keV, but can be traced up to 14 keV in some cases,
and has an average duration of 131(±103) s at 7–8 keV. The duration increases with decreasing photon energy. The peak count
rate defined by cross-correlation is delayed at low energies. The temperature peaks early in the event and then decreases,
whereas the emission measure increases throughout the event. The properties are consistent with thermal conduction dominating
the evolution. In some of the bigger events, a second component was found in the 11–14 keV range extending down to 8 keV in
some cases. The duration is typically 3 times shorter and ends near the peak time of the thermal component consistent with
the Neupert effect of regular flares. Therefore the second component is suggested to be of non-thermal origin, presumably
causing the beam-driven evaporation of the first component. The two components can be separated and analyzed in detail for
the first time. Low-keV measurements allow a reliable estimate of the energy input by microflares necessary to assess their
relevance for coronal heating.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1022496515506 相似文献
720.
Seismology of the solar atmosphere 总被引:1,自引:0,他引:1
Wolfgang Finsterle Stuart M. Jefferies Alessandro Cacciani Paolo Rapex Cynthia Giebink Allister Knox Vincenzo DiMartino 《Solar physics》2004,220(2):317-331
We describe a new instrument for seismically probing the properties of the Sun's lower atmosphere, and present some first
results from an observational campaign carried out at the geographic South Pole during the austral summer of 2002/2003. A
preliminary analysis of the data (simultaneous, high-cadence observations of the velocity signals from the photosphere and
low chromosphere) shows that the well-known suppression of acoustic power in regions of strong magnetic field, and enhancement
of high-frequency power around active regions (acoustic halos), are both consistent with a spreading out of the magnetic field
lines with increasing height in the atmosphere. The data have also revealed some unexpected wave behavior. First, evanescent-like
waves are found at frequencies substantially above the acoustic cut-off frequency in regions of intermediate magnetic field.
Second, upward- and downward-propagating waves are detected in areas of strong magnetic field such as sunspots and plage:
even at frequencies below the acoustic cut-off frequency. Third, the wave behavior in regions of strong magnetic field can
change over periods of a few hours from propagating to evanescent. While we have no concrete explanation for the first two
results, the latter result opens up the question of whether sound waves are involved in short-term events such as flares or
CME's. 相似文献