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101.
Remote sensing techniques using Landsat ETM+ applied to the detection of iron ore deposits in Western Africa 总被引:1,自引:0,他引:1
Andrea Ciampalini Francesca Garfagnoli Benedetta Antonielli Sandro Moretti Gaia Righini 《Arabian Journal of Geosciences》2013,6(11):4529-4546
Remote sensing methods enable the rapid and inexpensive mapping of surface geological and mineralogical features. This capability proves highly useful when working on isolated or inaccessible areas. In this study, several enhancements of Landsat Enhanced Thematic Mapper plus (i.e. band ratios, false colour composites and principal component analysis) were used and evaluated to obtain the best possible visualisation of iron deposits hosted in the Devonian sedimentary rocks of northwestern Africa. In particular, two test sites were chosen: southern Algeria (Djebilet area), where the literature mineralogical and geological data on iron mine fields were already available, and the Western Sahara (the southern flank of Tindouf Basin), which was investigated during a field campaign and was where the occurrence of an analogous sedimentary succession led us to hypothesise the possible presence of exploitable iron deposits. This work demonstrates the usefulness of multispectral imagery in the detection of iron-rich areas and establishes a full remote sensing procedure, which can be profitably applied to a wider region of Western Sahara and can provide interesting perspectives on the possibility of detecting new exploitable iron ore deposits in arid environments. 相似文献
102.
Alessia Viero Sandro Furlanis Cristina Squarzoni Giordano Teza Antonio Galgaro Piero Gianolla 《Landslides》2013,10(4):393-408
On October 12th, 2007 about 40,000 m3 of dolomitic rock detached from the northern wall of the peak known as “Cima Una” (Val Fiscalina, Sesto Dolomites, Bolzano, Italy), and fell 900 m to Fiscalina Valley below. The event generated a dense dust cloud, which traveled up to 4 km from the source area. The failure surface was formed by two near-vertical surfaces, almost perpendicular to each other. The orientation of these surfaces is consistent with two of the main regional tectonic sets. Only a small portion of the fallen material appeared to be preserved as blocks deposited at the base of the rock wall. About a fifth of the fallen mass was deposited on a colluvial cone. The missing mass, estimated to be about 80 %, may be represented by highly fragmented rock in part deposited as sand on the valley floor and in part dispersed as a dense dust cloud generated during the rockfall. There appears to be a deficit of deposited material, which could lead underestimation in the calculation of rock–cliff recession rates. The dynamics of the rockfall, strongly conditioned by the local topography, partially explains the intense rock breakage and the generation of the dust cloud. The rockfall was not caused by an external trigger, such as an earthquake or heavy rainfall; the failure was most likely progressive due to mechanical and physical degradation along highly stressed failure surfaces, possibly promoted by permafrost degradation and freeze and thaw processes. 相似文献
103.
104.
Atomic-scale mechanisms of plastic deformation in orthoenstatite, MgSiO3 are studied by computer simulation methods. The combined use of metadynamics and molecular dynamics allows a direct observation
of the structural changes during the creation of stacking faults in the (100) plane. A sequence of slip deformations in two
different (100) planes at P = 15 GPa and T = 1,000 K reveals a probable transformation mechanism for the ortho- to high-pressure clinopyroxene transition. Each of the
observed slips consists of at least four partial deformations crossing high-energy intermediate structures. In agreement with
experimental studies, both (100)[010] and (100)[001] slip systems are activated in the deformation process. The observation
of a dominant (100)[001] single slip system in pyroxenes may be related to the fact that high-energy intermediate dislocations
with (100)[010] component are not stable on geological or experimental timescales. 相似文献
105.
Avanzinelli Riccardo; Elliott Tim; Tommasini Simone; Conticelli Sandro 《Journal of Petrology》2008,49(2):195-223
We present new U-series isotope, 87Sr/ 86Sr, 143Nd/ 144Nd andtrace element data for a set of mafic, K-rich rocks from volcanoesin Central–Southern Italy. These shoshonitic to ultrapotassiclavas display strongly depleted high field strength element(HSFE) abundances with respect to other incompatible trace elementstogether with high but variable 87Sr/ 86Sr and low but variable143Nd/ 144Nd values. Such characteristics are thought to bedue to addition of subducted crust of variable amount and compositionto their mantle sources prior to magma genesis. Rocks from thenorthernmost region (i.e. Tuscan Magmatic Province and NorthernRoman Magmatic Province) display (230Th/ 238U) activity ratiosclose to radioactive equilibrium, suggesting that metasomatismof their sources occurred before 400 ka and recent melting tookplace at shallow depths, in the absence of garnet. A 238U excessof up to 27% has been measured in rocks from the NeapolitanDistrict. The occurrence of significant U excesses is a featureof arc magmas, but is typically seen in depleted lavas ratherthan in highly enriched rocks such as these (20 ppm Th). Thissignature requires a recent addition of a U-rich component tothe already strongly enriched mantle wedge beneath this regionof Italy. We suggest that a supercritical liquid, from deeplysubducted carbonate-rich sediments of the still-active Ionianslab, is responsible for generating a high-U, low-Th component,which produces the observed disequilibria. A 30% 230Th excessmeasured in a single unaltered sample from the Lucanian MagmaticProvince, along with a less marked negative HFSE anomaly, suggeststhe contribution of a deeper, garnet-bearing component in thegenesis of these magmas, plausibly related to the upwellingof asthenospheric mantle around the corner of the Ionian slab. KEY WORDS: U/Th disequilibria; potassic and ultrapotassic rocks; subduction: metasomatism; mantle melting; Central and Southern Italy 相似文献
106.
Sandro FADDA Alessandro RIVOLDINI Ignazio CAU 《Geostandards and Geoanalytical Research》1995,19(1):41-54
The microwave oven acid digestion technique has been routinely applied to the ICP-MS multielement analysis of whole powdered coal. Samples were treated with a mixture of HF/aqua regia/HClO4 in closed Teflon PFA vessels without any pre-treatment. Complete dissolution of the coal matrix is not required, but only one that results in quantitative and reproducible recovery of more than 40 trace elements with minimum digestion time, minimum use of reagents and minimal operator attendance. The precision of the analysis as well as the repeatability of the sample preparation procedure and precision of instrumental measurements have been evaluated. Eight coal standards, including NBS SRM 1632b, 3 South Africa Reference Materials (SARMs) 18 to 20 and 4 USA ARs 1800 to 1803 were analysed in this manner providing data for all the 14 rare earth elements along with others of geochemical interest, technological relevance as well as environmental and health concern. The results, from the ppb level to several ppm, are discussed for all the elements including detection and quantification limits, precision and accuracy. In general, good agreement was achieved with the certified and/or available published values. 相似文献
107.
Marina De Nicola Carmela Gambardella Sandro M. Guarino 《Marine pollution bulletin》1992,24(12):619-621
Separate and interactive pollution effects of Cd and Zn on electrophoretically-detected allozyme frequencies of the different genotypes at PGI and PGM loci were studied in Idotea baltica.
Differential survivorship of PGM genotypes was detected in the presence of the single or combined pollutants, while no effect was observed for PGI. Cadmium decreased heterozygosity while zinc or Cd + Zn increased it, suggesting an antithetic action of the two metals and the prevalence of zinc. 相似文献
108.
Sandro Da Silva Fernandes 《Celestial Mechanics and Dynamical Astronomy》1995,62(4):305-321
Some classic expansions of the elliptic motion — cosmE and sinmE — in powers of the eccentricity are extended to highly eccentric orbits, 0.6627...<e<1. The new expansions are developed in powers of (e–e*), wheree* is a fixed value of the eccentricity. The coefficients are given in terms of the derivatives of Bessel functions with respect to the eccentricity. The expansions have the same radius of convergence (e*) of the extended solution of Kepler's equation, previously derived by the author. Some other simple expansions — (a/r), (r/a), (r/a) sinv, ..., — derived straightforward from the expansions ofE, cosE and sinE are also presented. 相似文献
109.
110.
Occurrence of selected estrogens in mangrove sediments 总被引:1,自引:0,他引:1
Froehner S Machado KS Stefan E Bleninger T da Rosa EC Martins Cde C 《Marine pollution bulletin》2012,64(1):75-79
This paper presents results related to the occurrence and distribution of estrogens along the Brazilian coast. Three mangrove areas were chosen to evaluate the presence of estrogens in surface sediments of mangrove forests. The presence of estrogens was observed in all studied sites. 17-α-Ethinylestradiol (EE2), a synthetic estrogen, was the most common and has been found in higher concentration (0.45-129.78 ng/g) compared to 17-β-estradiol (E1) and estrone (E2) (both being natural estrogens). The concentrations of E1 and E2 ranged from 0.02 to 49.27 ng/g and 0.03 to 39.77 ng/g, respectively. Theoretically, under anaerobic conditions EE2 can be reduced to E1 even in environments such as sediments of mangrove forests, which are essentially anaerobic. Even if the concentrations of estrogens seem to be insignificant in some samples, the effects remain uncertain. 相似文献