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91.
Ingo Zank 《Boundary-Layer Meteorology》1980,19(4):487-493
This paper describes the influence of noise on the u, v, and w wind components, which are measured by commonly used rectangular hot-film or hot-wire probes. It is shown that the distortion of the u, v, and w turbulence spectra may be entirely different, even if all three measured cooling velocities are equally disturbed by the same noise signal. A practical formalism is given for estimating the influence of any cooling velocity noise on the spectra and cospectra of u, v, and w. With inverted matrices, the original spectrum of a noise signal in the cooling velocities can be calculated from the observed u, v, and w spectra, assuming that the undisturbed shape of them is known.This work was supported by the Sonderforschungsbereich Meeresforschung of the Deutsche Forschungsgemeinschaft. 相似文献
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A numerical evaluation of the accuracy of the standard balance equations (BE) and the asymmetric balance equations (AB) in strong vortex applications is presented. Linearized equations for the evolution of disturbances on a symmetric hurricane-like vortex in a shallow-water model are used to compare forecasts using the AB and BE formulations with benchmark primitive equation forecasts. The validity of the BE and AB models is formally determined by the square of the Froude number, F2, and the square of the local Rossby number for disturbances with azimuthal wavenumber n, , respectively. The numerical experiments demonstrate that accurate results can be achieved with BE and AB in situations where F2 and , respectively, are not necessarily small. When the divergence of the asymmetric disturbance is not much smaller than its vorticity, and the azimuthal wavenumber of the disturbance is low, the AB system proves to be a useful alternative to BE. 相似文献
97.
Wolfgang R. Jacoby Oliver Hartmann Herbert Wallner Peter L. Smilde Stefan Bürger Lars E. Sjöberg Sigurdur Erlingsson Detlef Wolf Volker Klemann Ingo Sasgen 《Pure and Applied Geophysics》2009,166(8-9):1283-1302
Repeated gravity measurements were carried out from 1991 until 1999 at sites SE of Vatnajökull, Iceland, to estimate the mass flow and deformation accompanying the shrinking of the ice cap. Published GPS data show an uplift of about 13 ± 5 mm/a near the ice margin. A gravity decrease of –2 ± 1 μGal/a relative to the Höfn base station, was observed for the same sites. Control measurements at the Höfn station showed a gravity decrease of –2 ± 0.5 µGal/a relative to the station RVIK 5473 at Reykjavík (about 250 km from Höfn). This is compatible, as a Bouguer effect, with a 10 ± 3 mm/a uplift rate of the IGS point at Höfn and an uplift rate of ~20 mm/a near the ice margin. Although the derived gravity change rates at individual sites have large uncertainties, the ensemble of the rates varies systematically and significantly with distance from the ice. The relationship between gravity and elevation changes and the shrinking ice mass is modelled as response to the loading history. The GPS data can be explained by 1-D modelling (i.e., an earth model with a 15-km thick elastic lithosphere and a 7·1017 Pa·s asthenosphere viscosity), but not the gravity data. Based on 2-D modelling, the gravity data favour a low-viscosity plume in the form of a cylinder of 80 km radius and 1017 to 1018 Pa·s viscosity below a 6 km-thick elastic lid, embedded in a layered PREM-type earth, although the elevation data are less well explained by this model. Strain-porosity-hydrology effects are likely to enhance the magnitude of the gravity changes, but need verification by drilling. More accurate data may resolve the discrepancies or suggest improved models. 相似文献
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Joy E. Reid Ingo Horn Henry P. Longerich Lance Forsythe George A. Jenner 《Geostandards and Geoanalytical Research》1999,23(2):149-155
Isotope dilution calibration has been applied to the determination of Zr and Hf in whole rocks by laser ablation (LA)-ICP-MS. Enriched isotopes were added during the preparation of flux-free, synthetic whole rock glasses and homogenised through a combination of grinding and fusion. This method avoids problems, such as solution instability and the chemical resistance of minerals such as zircon, inherent in acid digestion sample preparation. The use of isotope dilution removes the need for external calibration using certified reference material glasses such as NIST SRM 612 for which certified Zr and Hf values are not available. The precision of Zr and Hf determinations were found to be < 1% and 3.5% respectively, limited by Poisson counting statistics which contributed to 50% of the final precision of analysis. Measured values correlate closely with compiled literature values. 相似文献
100.
Ingo Horn Friedhelm von Blanckenburg Grit Steinhoefel 《Geochimica et cosmochimica acta》2006,70(14):3677-3688
The feasibility of in situ stable Fe isotope ratio measurements using UV-femtosecond laser ablation connected to a multiple-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) has been investigated. Different types of matrices, independently determined by solution MC-ICP-MS after chromatographic separation of Fe, have been analysed by laser ablation using the isotopically certified iron reference material IRMM-014 as the bracketing standard. The samples have been pure iron metal (JM Puratronic), Fe-meteorites (North Chile, Glenormiston and Toluca), the meteorite phases kamacite and taenite in Toluca and Fe-sulphides. Furthermore, Fe isotope ratios from hydrothermal hematite, siderite and goethite from an old mining area in the Schwarzwald, Germany, and of magnetite from the metamorphic Biwabik iron formation have been determined. The results show that a precision of better than 0.1‰ (2 sigma) can be achieved with laser ablation and that all the results obtained agree with those determined by solution ICP to better than 0.1‰. This precision and accuracy is achievable in both raster and spot ablation mode. A matrix-matched bracketing standard is not required , and all these materials can be measured accurately against a metal standard. The hydrothermal minerals show significant Fe isotope zonations. In some samples the range of δ56Fe in a single aggregate encompasses the entire spectrum of ratios found by bulk solution analyses in multiple samples distributed over the whole mining district. For example, isotopic zonations found in secondary fibrous hematites show a continuous change in the δ56Fe values from −0.5‰ in the core to −1.8‰ in the rim. Primary hydrothermal siderite shows the reverse pattern with lighter values in the core than in the rim. While the siderite is thought to record primary fluid histories, the hematite pattern is interpreted as a reworked isotopic signature generated by oxic dissolution of primary zoned siderite and immediate close range re-precipitation of the oxidized Fe. Abrupt changes are documented for secondary goethite showing a distinct overgrowth that is 0.4‰ lighter than the core of the grain. If indeed Fe isotopes in secondary minerals from hydrothermal ore deposits record the initial isotopic signatures of their precursor minerals, and these in turn record hydrothermal fluid histories, then the tools are in place for a detailed reconstruction of the deposit‘s genesis. We expect similar observations from other Fe-rich deposits formed at intermediate and low-temperatures (e.g. banded iron formations). Laser ablation now provides us with the spatial resolution that adds a further dimension to our interpretation of stable Fe-isotope fractionation. 相似文献