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81.
The geochemical composition of the terrestrial surface (without soils) and comparison with the upper continental crust 总被引:1,自引:0,他引:1
Jens Hartmann Hans H. Dürr Nils Moosdorf Michel Meybeck Stephan Kempe 《International Journal of Earth Sciences》2012,101(1):365-376
The terrestrial surface, the “skin of the earth”, is an important interface for global (geochemical) material fluxes between
major reservoirs of the Earth system: continental and oceanic crust, ocean and atmosphere. Because of a lack in knowledge
of the geochemical composition of the terrestrial surface, it is not well understood how the geochemical evolution of the
Earth’s crust is impacted by its properties. Therefore, here a first estimate of the geochemical composition of the terrestrial
surface is provided, which can be used for further analysis. The geochemical average compositions of distinct lithological
classes are calculated based on a literature review and applied to a global lithological map. Comparison with the bulk composition
of the upper continental crust shows that the geochemical composition of the terrestrial surface (below the soil horizons)
is significantly different from the assumed average of the upper continental crust. Specifically, the elements Ca, S, C, Cl
and Mg are enriched at the terrestrial surface, while Na is depleted (and probably K). Analysis of these results provide further
evidence that chemical weathering, chemical alteration of minerals in marine settings, biogeochemical processes (e.g. sulphate
reduction in sediments and biomineralization) and evaporite deposition are important for the geochemical composition of the
terrestrial surface on geological time scales. The movement of significant amounts of carbonate to the terrestrial surface
is identified as the major process for observed Ca-differences. Because abrupt and significant changes of the carbonate abundance
on the terrestrial surface are likely influencing CO2-consumption rates by chemical weathering on geological time scales and thus the carbon cycle, refined, spatially resolved
analysis is suggested. This should include the recognition of the geochemical composition of the shelf areas, now being below
sea level. 相似文献
82.
Multiple sources for mineralizing fluids in the Charmitan gold(-tungsten) mineralization (Uzbekistan) 总被引:1,自引:0,他引:1
Torsten Graupner Samuel Niedermann Dieter Rhede Ulf Kempe Reimar Seltmann C. Terry Williams Reiner Klemd 《Mineralium Deposita》2010,45(7):667-682
Mineral assemblages present within the Charmitan gold(-tungsten) quartz-vein mineralization have been investigated for their
cathodoluminescence behaviour, chemical composition and noble gas isotope systematics. This inventory of methods allows for
the first time a systematic reconstruction of the paragenetic relationships of quartz, scheelite, sulphides and native gold
within the gold mineralization at Charmitan and provides the basis to utilise noble gas data in the discussion of sources
and evolution of ore-forming fluids. The vein quartz is classified into four generations based on microscopic and cathodoluminescence
investigations. Quartz I shows intense brittle deformation as associated scheelite I. Undeformed scheelite II overgrows scheelite
I and has lower light rare earth element and higher intermediate rare earth element contents as well as higher strontium concentrations.
Scheelite II is associated with the economic gold mineralization and formed during re-crystallisation and re-precipitation
of material which was partly re-mobilised from early scheelite I during infiltration of gold-bearing fluids. Early stage native
gold inclusions are often associated with stage 2 sulphides, scheelite II and bismuth tellurides and contain Ag (3.6–24.4 wt.%),
Hg (≤1.0 wt.%) and Bi (≤0.2 wt.%). Later stage electrum grains occur in association with stage 3 sulphides and sulphosalts
and contain Hg (<0.8 wt.%) and elevated Sb concentrations (up to 3.0 wt.%). Noble gas isotope data (3He/4He: 0.2-0.4 Ra) for hydrothermal ore fluids trapped in the gold-related sulphides and sulphosalts (stage 2 pyrite and arsenopyrite;
stage 3 pyrite, sphalerite, galena and lead sulphosalts) suggest that diverse fluid sources were involved in the formation
of the Charmitan gold deposit. These data are indicative of a small, but significant input of fluids from external, deep-seated
(mantle and possibly lower crust) sources. A decrease in the input of mantle helium and an increasing role of crustal helium
from early to later stages of the mineralization is suggested by the measured 3He/4He and 40Ar*/4He ratios. Sulphides from ore veins in meta-sedimentary rocks contain higher portions of meteoric fluids than those in intrusive
rock types as indicated by their lower 3He/36Ar ratios. The 3He/36Ar ratios in the meta-sedimentary rocks agree well with ratios typical of gold mineralizations in the Tien Shan gold province
completely hosted by meta-sedimentary sequences, indicating intense fluid-wall rock interaction. 相似文献
83.
Ulf Söderlund Axel Hofmann Martin B. Klausen Johan R. Olsson Richard E. Ernst Per-Olof Persson 《Precambrian Research》2010
We present baddeleyite U–Pb ages of Neoarchaean to Palaeoproterozoic dyke swarms and the Mashonaland sill province in Zimbabwe. The 2575.0 ± 1.5 Ma age of the Umvimeela dyke is indistinguishable from the 2575.4 ± 0.7 Ma result (Oberthür et al., 2002) for a pyroxenite layer of the Great Dyke and testifies to synchronous emplacement of the Great Dyke and its satellites. Three samples of WNW- to NNW-trending dykes of the Sebanga swarm yielded ages of 2512.3 ± 1.8 Ma, 2470.0 ± 1.2 Ma and 2408.3 ± 2.0 Ma, the latter of which dates the Sebanga Poort Dyke of this swarm. These results suggest that emplacement took place over a protracted period which involved at least three generations of dykes within the swarm and, more importantly, invalidate previous inferences of a genetic link between the Sebanga swarm and the Mashonaland sills. Crystallisation ages of 1877 ± 2.2 Ma, 1885.9 ± 2.4 Ma and 1875.6 ± 1.6 Ma for three dolerite samples of the extensive Mashonaland sills from different parts of the Zimbabwe craton were also obtained. This is the oldest common igneous event that is recorded in the Zimbabwe and Kaapvaal cratons. Collectively with previous published geochronological and petrological evidence in favour of a major 2.0 Ga event within the Limpopo Belt, these results suggest that the Zimbabwe and Kaapvaal cratons did not form a coherent unit (Kalahari) until ca. 2.0 Ga. 相似文献
84.
431 oriented samples were collected from 27 dolerite dykes at 17 sites, belonging to 2.95, 2.65, and 1.90 Ga swarms, that trend SE, E and NE, respectively from the Bushveld Igneous Complex into the eastern Kaapvaal Craton (ages determined by Olsson et al., 2010; Olsson in Söderlund et al., 2010). Samples were analyzed for paleomagnetism and also anisotropy of magnetic susceptibility (AMS). For the 2.95 Ga SE-trending dykes high temperature/coercivity ‘P’ component has unblocking temperatures up to 590 °C and coercivity 40–90 mT and demonstrate SSW declination and intermediate positive inclination. Based on positive contact and conglomerate tests we argue for a primary origin of this component. The paleopole (BAD), calculated from ‘P’ component, does not correspond to any of the previously obtained Archean–Paleoproterozoic paleopoles for the Kaapvaal Craton, and represents a new key pole for 2.95 Ga. The high-coercivity ‘H’ component for the 2.65 Ga-old E-trending dykes has a SSW declination and steep positive inclination. Paleomagnetic pole (RYK), recalculated from this component, is close to the paleopoles, obtained by Wingate (1998) and Strik et al. (2007) for 2.78 Ga Ventersdorp volcanics. The third group, NE-trending dykes of the 1.90 Ga Black Hill swarm demonstrate an ‘M’ component with dual polarity high-coercivity component with SSE-declination and negative intermediate inclination. The paleopole (BHD), calculated from this component is close to the 1.87 Ga pole of the Kaapvaal Craton obtained by Hanson et al. (2004). Overprint directions include a very well developed thermo-chemical overprint (Dec = 329° Inc = −36°), which is believed to be associated with a ∼0.18 Ga regional ‘Karoo’ thermal event. 相似文献
85.
Saleh A.S. Yahya Martin Gullström Marcus C. ÖhmanNarriman S. Jiddawi Mathias H. AnderssonYunus D. Mgaya Ulf Lindahl 《Estuarine, Coastal and Shelf Science》2011,94(1):16-23
Degradation and mortality of corals is increasing worldwide and is expected to have significant effects on coral reef fish; hence studies on these effects are essential. In the present study, a field experiment was set up within Mafia Island Marine Park in Tanzania (East Africa) to examine the effects of bleaching and habitat structure on colonisation of coral reef fish assemblages. Live and bleached staghorn coral Acropora formosa was transplanted onto plots in a site dominated by sand and rubble, and the experimental design comprised of three treatments: live coral, bleached coral and eroded coral rubble. There was an immediate increase (within 24 h) in fish abundance and diversity in the two treatments with standing corals. Overall, live and bleached coral plots showed similar effects, but differed from the eroded coral plots which had a much lower abundance and diversity of fish. In general, fish species diversity changed with time over the study period while fish abundance did not. Multivariate analyses showed that while there were differences in fish assemblage structure between standing corals and the eroded coral treatment, there was neither a difference between live and bleached coral treatments nor any temporal effects on fish assemblage structure. Our findings suggest that physical structure and complexity of habitat have stronger effects on colonisation of reef fish assemblages than changes in coral health (such as bleaching) which do not affect coral structure. This may have important implications for appropriate coral reef management. 相似文献
86.
87.
88.
Hanna Hadler Andreas Vött Timo Willershäuser Dennis Wilken Ruth Blankenfeldt Claus von Carnap-Bornheim Kurt Emde Peter Fischer Ulf Ickerodt Stefanie Klooß Bente Majchczack Lea Obrocki Wolfgang Rabbel 《地球表面变化过程与地形》2021,46(15):3228-3251
In ad 1362, a major storm surge drowned wide areas of cultivated medieval marshland along the north-western coast of Germany and turned them into tidal flats. This study presents a new methodological approach for the reconstruction of changing coastal landscapes developed from a study site in the Wadden Sea of North Frisia. Initially, we deciphered long-term as well as event-related short-term geomorphological changes, using a geoscientific standard approach of vibracoring, analyses of sedimentary, geochemical and microfaunal palaeoenvironmental parameters and radiocarbon dating. In a next step, Direct Push (DP)-based Cone Penetration Testing (CPT) and the Hydraulic Profiling Tool (HPT) were applied at vibracore locations to obtain in situ high-resolution stratigraphic data. In a last step, multivariate linear discriminant analysis (LDA) was successfully applied to efficiently identify different sedimentary facies (e.g., fossil marsh or tidal flat deposits) from the CPT and HPT test dataset, to map the facies' lateral distribution, also in comparison to reflection seismic measurements and test their potential to interpolate the borehole and CPT/HPT data. The training dataset acquired for the key site from coring and DP sensing finally allows an automated facies classification of CPT/HPT data obtained elsewhere within the study area. The new methodological approach allowed a detailed reconstruction of the local coastal landscape development in the interplay of natural marsh formation, medieval land reclamation and storm surge-related land losses. 相似文献
89.
Ulf B��ntgen Rudolf Br��zdil Petr Dobrovolny Mirek Trnka Tom��? Kyncl 《Theoretical and Applied Climatology》2011,105(1-2):167-180
Past, present, and projected fluctuations of the hydrological cycle, associated to anthropogenic climate change, describe a pending challenge for natural ecosystems and human civilizations. Here, we compile and analyze long meteorological records from Brno, Czech Republic and nearby tree-ring measurements of living and historic firs from Southern Moravia. This unique paleoclimatic compilation together with innovative reconstruction methods and error estimates allows regional-scale May?CJune drought variability to be estimated back to ad 1500. Driest and wettest conditions occurred in 1653 and 1713, respectively. The ten wettest decades are evenly distributed throughout time, whereas the driest episodes occurred in the seventeenth century and from the 1840s onward. Discussion emphasizes agreement between the new reconstruction and documentary evidence, and stresses possible sources of reconstruction uncertainty including station inhomogeneity, limited frequency preservation, reduced climate sensitivity, and large-scale constraints. 相似文献
90.
Birger Ulf Hansen Niels Nielsen Ole Humlum Bent Hasholt 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(1):85-90
In october 1990 an automatic weather station was established at the Arctic Station (65° 15', 53°31'W), Qeqertarsuaq (Godhavn), Central West Greenland. The Station register parameters each 20 minutes, and the paramters have been described in an earlier paper in this journal by Nielsen et al.(1995). The present paper summarizes meteorological parameters during 1999. During a field campaign in 1999, woody remains from Salix glauca were found on a nunatak, 515 m. a.s.l. on the Mittivakkat Glacier, South East Greenland. Radio carbon dating determined the age of a wood sample to AD 640. Together with analyses of macroscopic botanical remains and insect rests in peaty material found nearby, these results indicate, that a warmer climate prevailed near the glacier around AD 600. These findings are in accordance with temperature records based on studies of ice cores from the Greenland Ice sheet. 相似文献