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71.
Igneous, metamorphic and biogenic apatite contains Lu and Hf in proportions that make this mineral suitable for dating by the 176Lu–176Hf method. We present a new method for separation of Lu and Hf from apatite that involves a single extraction column step for Hf and a second exchange column step for Lu. This procedure allows rapid sample processing prior to analysis by MC-ICP-MS. Results from the igneous Gardiner, Skaergaard and Khibina Intrusions indicate that the closure temperature for the Lu–Hf isotopic system in apatite is relatively high. The Lu–Hf isochron age of 60 Ma for the Skaergaard Intrusion, East Greenland, is older than the generally accepted emplacement age, but does not appear to be a product of mixing. A centimeter-sized apatite from the Otter Lake area, Grenvillian Province, yields high and variable 176Lu/177Hf ratios showing that metamorphic apatite may, in some cases, allow for mono-mineral dating. The most important application of the method is undoubtedly its potential use for dating sedimentary formations. Although we find biogenic apatite in porous matrix highly susceptible to post-depositional resetting of the Lu–Hf isotopic system, the preservation of a near-depositional age for a shark tooth from the impermeable London Clay and recent work on crystalline authigenic phosphorites [Earth Planet. Sci. Lett. 201 (2002) 203] show the Lu–Hf system to be a promising tool for direct dating of sedimentary formations. 相似文献
72.
An ultrafiltration methodology and the results of its application on Elbe river water are presented. Compared with other methods, Ultrafiltration allows fractionation of the molecular-weight fractions of DOC for higher volumes of solution in a shorter time. To characterize the molecular-weight fractions, the sum parameter DOC (β(DOC)) and the absorption coefficient at 254 nm a254 were measured, together with determination of a254/ β(DOC) for further characterization of the DOC fractions and to provide information about changes in parts of the UV-active substances of the total dissolved organic material. In the period May 1992 to November 1994, the DOC molecular-weight composition of 65 samples of Elbe river water were determined. At two sampling locations (Torgau-East and Meissen), the DOC content β(DOC) was approximately 6 mg/L. The high-molecular weight fraction (> 10000 g/mol) gave a mean of 13% of the total DOC content β0(DOC). The measurements showed that the molecular composition of DOC in the Elbe does not greatly differ. There was also no clear seasonal influence on the molecular-weight composition of the DOC content. During the period of investigation, the percentage part of β(DOC) and a254/β(DOC) of the high-molecular weight fraction of the total dissolved organic material increased, while the a254/β(DOC) values of the middle molecular-weight fraction remained fairly constant. The dependence of β(DOC) on discharge of the Elbe river is low. Changes in molecularweight composition of DOC were only observed during the steepest increase in river discharge during a flood event, with another spectrum of substances responsible for the increase in β(DOC) when compared with the β(DOC) for low or middle water level. 相似文献
73.
Influence of the Temperature on the Formation of Magnetite as an Additive for Magnetic Separation To investigate the influence of the temperature on the formation of magnetite in aqueous solution, experiments were performed in which ferrous hydroxide was precipitated from oxygen-free ferrous sulfate solution (c0(Fe) = 5 mmol·dm?3) and subsequently oxidized with synthetic air. The precipitates so obtained are a mixture of solids whose compositions depend on the temperature and on the rate of aeration. Above all, magnetite, goethite, and δ-FeOOH had been formed. Magnetite occurs at temperatures above about 15 °C, goethite above 35 °C, and δ-FeOOH below about 10 °C. Referring to the thermogravimetric plots and to the relationship between the temperature of formation and the pH measured upon completion of the reaction, it is justified to assume that also sulfate is contained in the precipitates. The values of the magnetic moment of the precipitates, which are crucial in magnetic separation, made evident the dependence on the temperature of formation expected on the basis of solid analyses and confirmed the presence of δ-FeOOH at rather low temperatures. At the rates of aeration applied, it was possible to obtain from about 15 °C on solids having magnetic moments which are sufficient for magnetic separation. 相似文献
74.
75.
Systematics of zircon crystallisation in the Cretaceous Separation Point Suite, New Zealand, using U/Pb isotopes, REE and Ti geothermometry 总被引:5,自引:3,他引:2
Robert Bolhar Steve D. Weaver J. Michael Palin Jim W. Cole Lorraine A. Paterson 《Contributions to Mineralogy and Petrology》2008,156(2):133-160
Plutonic zircons from the Cretaceous Separation Point Suite (SPS) were analysed by LA-ICPMS for U–Pb isotope ratios and trace
element concentrations. Pooled 206Pb/238U ages range from 112 to 124 Ma. Cathodoluminescence imaging reveals minor inheritence and textural evidence of repeated dissolution
and re-precipitation of zircon. Core and rim spot analyses, however, document zircon growth during extended periods of time
(>2 myr). Protracted crystallisation histories for simple plutonic systems are inconsistent with generalised thermal constraints,
which predict cooling below the solidus within <1 myr. Consequently, we conclude that the SPS granitoids sampled in this study
were not emplaced rapidly but incrementally over extended time periods. Zircon Th/U and Zr/Hf ratios are positively correlated
with crystallisation temperatures, consistent with crystallisation from evolving melts. However, highly variable trace element
concentrations, along with temperature reversals are indicative of complex crystallisation histories involving continuous
fractional crystallisation repeatedly punctuated by hotter, more mafic magma recharge. Normalised abundances of the redox-sensitive
elements Eu and Ce in zircon vary systematically with degrees of whole rock differentiation, pointing to evolutionary trends
in magmatic oxidation states coupled with feldspar crystallisation. 相似文献
76.
We thank H. Mashima for his interest in our recent article in Tectonophysics [Kim, H.J., Lee, G.H., Jou, H.T., Cho, H.M., Yoo, H.S., Park, G.T., Kim, J.S., 2007, Evolution of the eastern margin of Korea: Constraints on the opening of the East Sea (Japan Sea). Tectonophysics 436, 37–55.] and welcome the opportunity to respond to his comments. In our article we suggested that the southern part of the East Sea (Japan Sea) opened principally in the southeast direction in response to the northwestward subduction of the Pacific Plate beneath the Japan Arc. In contrast, Mashima claims that the opening of the East Sea was achieved in the south–southeast direction. However, there are many crucial things in his comments that we find scientifically unconvincing and misleading. In this reply, we give a detailed response to his comments. 相似文献
77.
In order to separate the scattering effect from intrinsic attenuation, we need a multiple scattering model for seismic wave propagation in random heterogeneous media. In paper I (Wu, 1985), radiative transfer theory is applied to seismic wave propagation and the energy density distribution (or the average intensity) in space for a point source is formulated in the frequency domain. It is possible to separate the scattering effect and the absorption based on the measured energy density distribution curves. In this paper, the data from digital recordings in the Hindu Kush region are used as an example of application of the theory. We also discuss two approximate solutions of coda envelope in the time domain: the single scattering approximation and the diffusion approximation and discuss the relation with the frequency domain solution. We point out that in only two cases can the apparent attenuation be expressed as an exponential decay form. One is thedark medium case, i.e., whenB
00.5, whereB
0 =
s
/(
s
+
a
) is the seismic albedo,
s
is the scattering coefficient,
a
is the absorption coefficient. In this case the absorption is dominant, the apparent attenuationb can be approximated by the coherent wave attenuationb =
s
+
a
. The other case is thediffuse scattering regime, i.e., whenB
00.5 (bright medium) andRL
s
,t
s
, whereR andt are the propagation distance and lapse time,L
s
and
s
are the scattering lengths (mean free path) and scattering time (mean free time), respectively. However, in this case the envelope decays with a rate close to the intrinsic attenuation, while the intensity decreases with distance with a coefficientb d
0(
s
+
a
) d
s
s
, whered
0 andd
s
are the diffusion multipliers (0<d
0,d
s
<1).For the Hindu Kush region, by comparing the theory with data from two digital stations of 53 events distributed up to depths of 350 km, we find that the scattering is not the dominant factor for the measured apparent attenuation ofS waves in the frequency range 2–20 Hz. From the observation on high frequency (f>20 Hz) seismograms, we suggest the existence of a stron-scattering surface layer with fine scale heterogeneities in the crust, at least for this region. 相似文献
78.
79.
Lars D. Hylander David Plath Conrado R. Miranda Sofie Lücke Jenny Öhlander Ana T. F. Rivera 《洁净——土壤、空气、水》2007,35(1):52-61
This case study performed at the largest gold mining village in the Philippines compares four methods for gold recovery: amalgamation, cyanide leaching, a shaking sluice, and Cleangold® sluices. The results show that a combination of manual panning or Cleangold® sluices followed by cyanidation is the best solution under present conditions, followed by cyanidation alone. Based on the knowledge obtained, remarks on suitable policy actions, which may be applied also in other gold fields, are made. 相似文献
80.