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31.
We have produced detailed maps of U and Th isotopes for three cross-sections of an Early Pleistocene equid tooth from the archaeological site of Fuente Nueva-3 (Orce, Andalusia, Spain). This permits us to visualise, for the first time, U migration processes in 3 dimensions. The tooth shows a concentration gradient from the top to the base, indicating the U profile had not equilibrated after >1 Ma. The spatial pattern of 230Th/234U and 234U/238U indicates complex U-mobilisation processes over the last 100 ka, dominated by small-scale redistribution of U. Leaching from the tooth through the pulp cavity started at least 93 ka ago with several later phases in various domains of the dentine and cement. This leaching event could have been triggered by changes in the local hydrological regime associated with periods of increased erosion in the Guadix-Baza basin. The results illustrate the difficulty of dating faunal material from Early Pleistocene sites. They also demonstrate that dental tissues can neither be considered as homogeneous media for U-diffusion, nor behave as closed systems for U-series isotopes because diagenetic alterations seem to trigger U-migration. The results do not support the notion that U-uptake into dental tissues is necessarily of short duration. Nevertheless, rapid laser ablation scanning can be used to identify suitable samples for dating as well as domains within the teeth that may have preserved original isotopic signatures, i.e. domains that have not been affected by recent U-mobilisation process. 相似文献
32.
Etienne Balan Simon Delattre Damien Roche Loïc Segalen Guillaume Morin Maxime Guillaumet Marc Blanchard Michele Lazzeri Christian Brouder Ekhard K. H. Salje 《Physics and Chemistry of Minerals》2011,38(2):111-122
The crystallinity of natural and synthetic apatite samples is often determined from the broadening of ν
4 PO4 infrared absorption bands. However, various physical mechanisms contribute to the observed linewidth. In the present study,
the factors determining the linewidth in the powder spectrum of synthetic fluorapatite and hydroxyapatite samples are investigated.
The temperature dependence of the infrared spectrum (10–270 K) is used to assess the respective contributions of homogeneous
broadening, related to the decay of phonons through anharmonic coupling, and heterogeneous broadening related to elastic strain
and macroscopic electrostatic effects. This latter contribution is dominant in the investigated samples and depends on the
shape of powder particles. It is discussed under the light of the theoretical modeling of the low-frequency dielectric properties
of apatite based on first-principles density functional theory calculations. The linewidth of the weak ν
1 PO4 absorption band provides a reliable information on microscopic sources of broadening, i.e., apatite crystallinity. In comparison,
the other more intense PO4 bands are more sensitive to long-range electrostatic effects. 相似文献
33.
34.
The inclination (I), declination (D) and total intensity (F) of the geomagnetic field were measured on Mount Etna in 1989-1991 at a dozen sites previously sampled for archeomagnetic studies. The purpose of the work was to determine the variations of these parameters at 30 cm above ground level, and how the distortion from the main field can affect the archeomagnetic record of volcanic rocks. Ten measurements were usually performed at each site with a three-component flux-gate magnetometer, whose estimated precision is ±0.2° on direction and ±50 nT on intensity. This was considered sufficient on volcanic areas with highly magnetized rocks and where the geomagnetic gradient may be in excess of 1000 nT/m. Results averaged for each site generally show small variations in intensity (±3% of the total field) and direction (±1.5°). The averaged values of the 12 sites (I=52.6°, D=0.3°, F=44010 nT) are very close to those measured in sedimentary terrain away from the volcano (I=52.9°, D=0.35°, F=44110 nT), themselves consistent with the interpolated IGRF in eastern Sicily. The largest deviations of the geomagnetic direction have been observed on four sites, three of them located on the South flank between 1900 and 700 m elevation. It is suggested that these anomalies are mainly related to dyke swarms which are common within the South Rift Zone of Mount Etna. Our findings show that reliable archeomagnetic results can be obtained from volcanic rocks, provided that lavas of the same eruption are sampled on several sites distributed over the largest possible area. 相似文献
35.
Lithosphere created in an interarc basin is expected to be characterized by features distinguishing it from “normal” oceanic lithosphere. Apart from island-arc geochemical affinities and from the occurrence of hydrous high-T parageneses in the mantle and deep crustal sequences, it is expected that due to a low rate of spreading, vertical transport prevails over lateral drifting.
The Canyon Mountain complex located in an island-arc environment of Permo-Triassic age offers a remarkable illustration of these expected geological characteristics. In particular, mantle diapirism is deduced from the structural study. Smaller diapirs are formed in crustal formations. The intrusions took place at variable temperatures (1300°–800°C) and were accompanied by multistage melting in hydrous conditions. 相似文献
36.
37.
Olivier Pourret Aline DiaMélanie Davranche Gérard GruauOdile Hénin Maxime Angée 《Applied Geochemistry》2007
Ultrafiltration experiments using new small ultracentifugal filter devices were performed at different pore size cut-offs to allow the study of organo-colloidal control on metal partitioning in water samples. Two shallow, circumneutral pH waters from the Mercy site wetland (western France) were sampled: one dissolved organic carbon (DOC)- and Fe-rich and a second DOC-rich and Fe-poor. Major- and trace-element cations and DOC concentrations were analysed and data treated using an ascendant hierarchical classification method. This reveals the presence of three groups: (i) a “truly” dissolved group (Na, K, Rb, Ca, Mg, Ba, Sr, Si and Ni); (ii) an inorganic colloidal group carrying Fe, Al and Th; and (iii) an organic colloidal group enriched in Cr, Mn, Co, Cu and U. However, REE and V have an ambivalent behaviour, being alternatively in the organic pool and in the inorganic pool depending on sample. Moreover, organic speciation calculation using Model VI were performed on both samples for elements for which binding constants were available (Ca, Mg, Ni, Fe, Al, Th, Cr, Cu, Dy, Eu). Calculation shows relatively the same partitioning of these elements as ultrafiltration does. However, some limitations appear such as (i) a direct use of ultrafiltration results which tends to overestimate the fraction of elements bound to humic material in the inorganic pool as regards to model calculations as well as, (ii) a direct use of speciation calculation results which tends to overestimate the fraction of elements bound to humic material in the organic pool with regard to ultrafiltration results. Beside these limitations, one can consider that both techniques, ultrafiltration and speciation calculation, give complementary information, especially for more complex samples where inorganic and organic colloids compete. 相似文献
38.
Richard Giot Sylvie Granet Maxime Faivre Nadia Massoussi Julie Huang 《Geomechanics and Geoengineering》2018,13(4):246-263
A transversely isotropic thermo-poroelastic constitutive law is developed and implemented in the finite element code Code_Aster (EDF, France). It is then validated using an analytic solution for an inclined borehole in a transversely isotropic medium. A strategy for identifying the parameters of the transversely isotropic thermo-poroelastic model based on an inverse method is proposed on the basis of different laboratory tests. To demonstrate the efficiency and applicability of the model, it is then applied in a three-dimensional numerical model of an underground structure in a parameter sensitivity study. The results of the modelling highlight the importance of accounting for anisotropic phenomena when determining the dimensions of underground facilities. The whole approach is presented in the paper, from model development to application to 3D numerical modelling to an engineering case study. 相似文献
39.
Didier Lahondère Florence Cagnard Guillaume Wille Jéromine Duron Maxime Misseri 《Environmental Earth Sciences》2018,77(10):385
This paper provides new mineralogical and morphological characterizations of calcic amphiboles from hydrothermally altered dolerites from France to discuss their potential to contain naturally occurring asbestos (NOA) and to release elongated mineral particles corresponding to asbestos fibers, or asbestos-like fibers, into the air. The calcic amphiboles were characterized using electron microprobe analysis, scanning and transmission electron microscopy. The results underline that fibrous occurrences of actinolite and ferro-actinolite regularly occur in hydrothermally altered dolerites, both in the groundmass and in quartz veins. In the groundmass, actinolitic amphiboles crystallize at the expense of magmatic clinopyroxenes and are rarely fibrous. Conversely, actinolite and ferro-actinolite fibers from quartz veins are potentially asbestiform to clearly asbestiform. The identification of quartz veins in hydrothermally altered dolerites is, therefore, an important parameter which should draw attention to the possible presence of asbestiform actinolite fibers. The mineralogical characterization of such veins as well as the estimation of their thickness and density is an important point to consider during studies involving NOA issues. Moreover, the degree of weathering of the dolerites, which directly affects the ability of non-asbestiform actinolite crystals to dissociate into very thin fibers, regarded as cleavage fragments instead of as asbestos, is also a key parameter to consider. Hydrothermally altered dolerites are common rocks likely to be exploited by the quarrying industry to produce aggregates or to be affected by construction works. Due to the abundance of actinolite fibers that they may contain locally, these rocks become priority targets to be monitored in terms of geological characterization and airborne fiber emission to ensure the protection of populations and workers. 相似文献
40.
Emmanuel Jacquet Maxime Piralla Pauline Kersaho Yves Marrocchi 《Meteoritics & planetary science》2021,56(1):13-33
We report microscopic, cathodoluminescence, chemical, and O isotopic measurements of FeO‐poor isolated olivine grains (IOG) in the carbonaceous chondrites Allende (CV3), Northwest Africa 5958 (C2‐ung), Northwest Africa 11086 (CM2‐an), and Allan Hills 77307 (CO3.0). The general petrographic, chemical, and isotopic similarity with bona fide type I chondrules confirms that the IOG derived from them. The concentric CL zoning, reflecting a decrease in refractory elements toward the margins, and frequent rimming by enstatite are taken as evidence of interaction of the IOG with the gas as stand‐alone objects. This indicates that they were splashed out of chondrules when these were still partially molten. CaO‐rich refractory forsterites, which are restricted to ?17O <?4‰ likely escaped equilibration at lower temperatures because of their large size and possibly quicker quenching. The IOG thus bear witness to frequent collisions in the chondrule‐forming regions. 相似文献