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81.
E. Sánchez-Ayaso J. A. Combi J. F. Albacete Colombo J. López-Santiago J. Martí A. J. Mu?oz-Arjonilla 《Astrophysics and Space Science》2012,337(2):573-579
We report XMM-Newton observations of the Galactic supernova remnant G296.8-0.3, together with complementary radio and infrared data. The spatial
and spectral properties of the X-ray emission, detected towards G296.8-0.3, was investigated in order to explore the possible
evolutionary scenarios and the physical connexion with its unusual morphology detected at radio frequencies. G296.8-0.3 displays
diffuse X-ray emission correlated with the peculiar radio morphology detected in the interior of the remnant and with the
shell-like radio structure observed to the northwest side of the object. The X-ray emission peaks in the soft/medium energy
range (0.5–3.0 keV). The X-ray spectral analysis confirms that the column density is high (N
H∼0.64×1022 cm−2) which supports a distant location (d>9 kpc) for the SNR. Its X-ray spectrum can be well represented by a thermal (PSHOCK) model, with kT∼0.86 keV, an ionization timescale of 6.1×1010 cm−3 s, and low abundance (∼0.12 Z
⊙). The 24 μm observations show shell-like emission correlated with part of the northwest and southeast boundaries of the SNR.
In addition a point-like X-ray source is also detected close to the geometrical center of the radio SNR. The object presents
some characteristics of the so-called compact central objects (CCO). Its X-ray spectrum is consistent with those found at
other CCOs and the value of N
H is consistent with that of G296.8-0.3, which suggests a physical connexion with the SNR. 相似文献
82.
Gianluca Sottili Danilo M. Palladino Mario Gaeta Matteo Masotta 《Bulletin of Volcanology》2012,74(1):163-186
Maar volcanoes represent a common volcano type which is produced by the explosive interaction of magma with external water.
Here, we provide information on a number of maars in the ultrapotassic Sabatini Volcanic District (SVD, Roman Province) as
young as ∼90 ka. The SVD maars are characterised in terms of crater and ejecta ring morphologies, eruptive successions and
magma compositions, in light of the local substrate settings, with the aim of assessing magma–water interaction conditions,
eruption energetics and genetic mechanisms. Feeder magmas spanned the whole SVD differentiation trend from trachybasalts–shoshonites
to phonolites. From the ejected lithic fragments from aquifer rocks, the range of depth of magma–water explosive interaction
is estimated to have been mostly at ∼400–600 m below ground level, with a single occurrence of surficial interaction in palustrine–lacustrine
environment. In particular, the interaction with external water may have triggered the explosive behaviour of poorly differentiated
magmas, whereas it may have acted only as a late controlling factor of the degree of fragmentation and eruption style for
the most differentiated magma batches during low-flux ascent in an incipiently fragmented state. Crater sizes, ejecta volumes
and ballistic data allow a reconstruction of the energy budget of SVD maar-forming eruptions. Erupted tephra volumes from
either monogenetic or polygenetic maars ranged 0.004–0.07 km3 during individual maar-forming eruptions, with corresponding total magma thermal energies of 8 × 1015–4 × 1017 J. Based on energy partitioning and volume balance of erupted magmas and lithic fractions vs. crater holes, we consider the
different contributions of explosive excavation of the substrate vs. subsidence in forming the SVD maar craters. Following
available models based on crater sizes, highly variable fractions (5–50%) of the magma thermal energies would have been required
for crater excavation. It appears that subsidence may have played a major role in some SVD maars characterised by low lithic
contents, whilst substrate excavation became increasingly significant with increasing degrees of aquifer fragmentation. 相似文献
83.
Greg G. Sass Stephen R. Carpenter Jereme W. Gaeta James F. Kitchell Tyler D. Ahrenstorff 《Aquatic Sciences - Research Across Boundaries》2012,74(2):255-266
Lakeshore residential development (LRD) reduces coarse woody habitat (CWH) in lakes resulting in negative effects on fishes.
We tested whether the addition of CWH could reverse those effects. We added CWH to Camp Lake, a lake with CWH abundances similar
to developed lakes, following 2 years of study of the fish populations in the reference and treatment basins. Both basins
were monitored for 4 years following the manipulation. Specifically, we tested for changes in the population dynamics (densities,
size-structure, growth), diet, and behavior (habitat use) of bluegill (Lepomis macrochirus) and largemouth bass (Micropterus salmoides). CWH addition had no discernible effect on fish population dynamics. Diet and behavioral responses were more pronounced
in the treatment basin. Prey diversity and availability increased. Piscivory increased, with decreased reliance upon terrestrial
prey, for largemouth bass. Habitat use was positively correlated with CWH branching complexity and abundance. Our study suggests
that negative effects observed in fish populations through CWH reductions cannot be reversed in the short-term by adding CWH.
We recommend that regulations governing the LRD process be protective of CWH. 相似文献
84.
85.
Rita C. S. von Randow Celso von Randow Ronald W. A. Hutjes Javier Tomasella Bart Kruijt 《Theoretical and Applied Climatology》2012,109(1-2):205-220
Considering the high rates of evapotranspiration of Amazonian forests, understanding the impacts of deforestation on water loss rates is important for assessing those impacts on a regional and global scale. This paper quantifies evapotranspiration rates in two different pasture sites in Amazonia and evaluates the differences between the sites. In both places, measured evapotranspiration varies seasonally, decreasing during the dry season. The decrease is higher at the southwestern Amazonia site, while at the central Amazonia site, the decrease is less pronounced. During the dry season, average values of evapotranspiration are around 2.2?±?0.6?mm?day?1 in central Amazonia and 2.4?±?0.6?mm?day?1 in southwestern Amazonia, while during the wet season, those values are 2.1?±?0.6?mm?day?1 in central Amazonia and 3.5?±?0.8?mm?day?1 in southwestern Amazonia. On an annual basis, the pasture in southwestern Amazonia has higher evapotranspiration than in central Amazonia. We conclude that the main reason for this difference is the lower available energy in the wet season at the central Amazonian site, combined with a lower leaf area index at this site during the whole year. Still, the evapotranspiration is significantly controlled by the vegetation, which is well coupled with the local moisture conditions in the dry season. 相似文献
86.
87.
Guarino Vincenza Wu Fu-Yuan Melluso Leone de Barros Gomes Celso Tassinari Colombo Celso Gaeta Ruberti Excelso Brilli Mauro 《International Journal of Earth Sciences》2017,106(6):1963-1989
International Journal of Earth Sciences - The Catalão II carbonatitic complex is part of the Alto Paranaíba Igneous Province (APIP), central Brazil, close to the Catalão I complex.... 相似文献
88.
G. Colombo 《Icarus》1971
This paper presents evidence suggesting that Jupiter's seven outer satellites, which exist in two distinct groups, were formed by a single collision of an asteroid and a larger satellite. 相似文献
89.
In this paper we discuss the uncommon case of an energetic, pyroclastic-flow-forming eruption with a SiO2-poor (42-45 wt.%), K-foiditic magma composition. The Trigoria-Tor de' Cenci Tuff (TTC; 561 ka) is the product of the first large-scale explosive event (of the order of 1-10 km3 of erupted products) in the Alban Hills Volcanic District, near the city of Rome, Italy. After an initial Plinian phase that produced a scoria fall horizon, pyroclastic current activity emplaced ash deposits with leucite-bearing juvenile scoria lapilli. The abundance of accretionary lapilli, the most distinctive feature of these deposits, together with the high degree of fragmentation, the abundance of minute lithic inclusions and the morphology of ash particles, indicates a hydromagmatic character for the most part of the eruption. The absence of vent-derived carbonate lithic clasts from the deep regional aquifer and the abundance of cognate lithic fragments suggest that the interaction with external water involved a surficial aquifer in the older Alban Hills volcanic terrains. Perhaps the most striking aspect of the TTC is the K-foiditic composition of the pre-eruptive melt, which, to our knowledge, is unique among explosive events of comparable size elsewhere in the world. The pre-eruptive magma system feeding the TTC was controlled mainly by leucite+clinopyroxene fractionation under aH2O<1 conditions. The low SiO2 activity prevented plagioclase and K-feldspar crystallization. The depth of the magma chamber can be estimated at 3-6 km within the carbonate substrate. In contrast to the other major pyroclastic-flow-forming eruptions of the Alban Hills, the juvenile volatile exsolution due to magma crystallization is not seen as the main mechanism driving the TTC eruption. We suggest that the explosive behaviour of the TTC magma in the early magmatic phase resulted from a rapid decompression due to a regional seismic event and from magma-water interaction in the succeeding phase. 相似文献
90.
Deriving drainage networks and catchment boundaries: a new methodology combining digital elevation data and environmental characteristics 总被引:3,自引:0,他引:3
Digital data on the position and characteristics of river networks and catchments are important for the analysis of pressures and impacts on water resources. GIS tools allow for the combined analysis of digital elevation data and environmental parameters in order to derive this kind of information. This article presents a new approach making use of medium-resolution digital elevation data (250-m grid cell size) and information on climate, vegetation cover, terrain morphology, soils and lithology to derive river networks and catchments over extended areas.In general, methods to extract channel networks at small scale use a constant threshold for the critical contributing area, independent of widely varying landscape conditions. As a consequence, the resulting drainage network does not reflect the natural variability in drainage density. To overcome this limitation, a classification of the landscape is proposed. The various data available are analysed in an integrated approach in order to characterise the terrain with respect to its ability to develop lower or higher drainage densities, resulting in five landscape types. For each landscape type, the slope–area relationship is then derived and the critical contributing area is determined. In the subsequent channel extraction, a dedicated critical contributing area threshold is used for each landscape type.The described methodology has been developed and tested for the territory of Italy. Results have been validated comparing the derived data with river and catchment data sets from other sources and at varying scales. Good agreement both in terms of river superimposition and drainage density could be demonstrated. 相似文献