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31.
Results of electrical conductivity measurments on synthetic olivines of the system Mg2SiO4Fe2SiO4 and on minerals of Dreiser Weiher peridotite nodule Ib-8 (Eifel, Germany) are discussed in relation to the measuring procedure and to the variation of thermodynamic parameters.The measurements were performed in solid state high-pressure vessels between 340 and 1100°C and at a pressure of 10 kbar. It is shown that for ternary olivines and for pyroxenes, the control of two further variables, like the chemical activities of the components, is needed besides temperature and pressure control. The experimental set-up for the control of chemical activities and oxygen partial pressure is shown. From the slopes of the lines of log σ against 1/T the activation energies were calculated. Though in most cases the same oxygen fugacity ?O2 is applied, the results reveal different values for synthetic and natural samples since the chemical activities of SiO2 are different. 相似文献
32.
G. Will L. Cemič E. Hinze K. -F. Seifert R. Voigt 《Physics and Chemistry of Minerals》1979,4(2):189-197
Electrical conductivities of Ni2SiO4, Fe2SiO4, and MgSiO3 were measured on synthetic powders in the temperature range 340° to 1,100° C and at pressures up to 20 kbars. For ternary compounds such as olivines and pyroxenes the control of two further variables, like the chemical activities of two components are needed, besides temperature and pressure. The activities of the corresponding binary oxides were controlled by equilibrating the samples with their neighbour-phases. Control of the oxygen partial pressure was achieved by buffer techniques. From the slopes of the lg σ vs. 1/T lines the activation energies were calculated for 10 kbar: 0.56 eV and 2.7 eV for Ni2SiO4 in equilibrium with SiO2 and Ni/NiO-buffer for the temperature range 500°–800°C and 800°–1,000°C resp. 0.52 eV for Fe2SiO4 in equilibrium with SiO2 and metallic iron, and 0.38 eV in equilibrium with SiO2 and magnetite; 1.11 eV for MgSiO3 in equilibrium with SiO2, and 1.25 eV in equilibrium with Mg2SiO4. 相似文献
33.
The dependence of Mg/Fe ordering on oxygen partial pressure in natural olivine crystals of volcanic origin has been studied by X-ray diffraction. Two natural crystals with 10% and 12% fayalite have been investigated and the atomic positions, anisotropic temperature factors, extinction coefficients and site occupancies have been refined, reaching R-values of 2.2%. After subjecting the crystals to oxygen partial pressures of 10?16 bar and 10?21 bar the crystals were studied again. In total six crystals were studied and the distribution coefficients K D determined. The natural untreated crystals had K D=1.09 and 1.06, e.g., a slight preference of Fe in (M1). p(O2) of 10?16 bar increased the ordering of Fe in (M1) to K D=1.2, while p(O2)=10?21 bar reversed K D to 0.8 with ordering of Fe in (M2). These experiments suggest that Mg/Fe ordering in olivines is primarily determined by the prevailing oxygen partial pressure. 相似文献
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35.
Barry R. Bickmore Christopher J. Tadanier Will D. Monn 《Geochimica et cosmochimica acta》2004,68(9):2025-2042
Bond-valence methods for the prediction of (hydr)oxide solution monomer and surface functional group acidity constants are examined in light of molecular structures calculated using ab initio methods. A new method is presented that is based on these calculated structures, and it is shown that previously published methods have neglected one or more of four essential features of a generalized model. First, if the apparent pKa values of solution monomers are to be used to predict intrinsic pKa values of surface functional groups, similar electrostatic corrections must be applied in both cases. In surface complexation models, electrostatic corrections are applied by representing a charged surface as a uniform plane of charge density, and an analogous correction can be made to solution monomers by treating them as charged spheres. Second, it must be remembered that real surfaces and real monomers are not homogeneous planes or spheres. Rather, charge density is distributed rather unevenly, and a further electrostatic correction (which is often quite large) must be made to account for the proximity of electron density to the point of proton attachment. Third, the unsaturated valence of oxygen atoms in oxyacids, hexaquo cations, and oxide surfaces is strongly correlated with acidity after electrostatic corrections are made. However, calculation of unsaturated valence for oxyacids and oxide surfaces must be based on realistic MeO bond lengths (taking into account bond relaxation), which can be obtained from ab initio structure optimizations. Finally, unsaturated valence must be divided between possible bonds (four for oxygen atoms) to reflect the fact that O-H bonds are localized to particular regions of the O atoms.Empirical models that take all these factors into account are presented for oxyacids and hexaquo cations. These models are applied to the gibbsite (100), (010), (001), and cristobalite (100) surfaces, and it is demonstrated that the model for oxyacids predicts reasonable intrinsic pKa values for oxide surfaces. However, the prediction of surface pKa values is complex, because the protonation state of one functional group affects the pKa values of neighboring groups. Therefore, calculations of larger periodic systems, progressively protonated and reoptimized, are needed. 相似文献
36.
The paper compares pole figure determinations with neutron diffraction and X-ray diffraction on experimentally deformed carbonate rocks, a coarse grained marble and fine grained limestone. Neutron diffraction enables determination of complete pole figures on a single spherical specimen and is advantageous for coarse grained materials. Results obtained with both diffraction techniques agree satisfactorily, although uncertainties introduced by counting statistics are more serious for neutrons than for X-rays. Continuous detectors add new possibilities which are still little explored. 相似文献
37.
Roberto De Propris Matthew Colless Simon P. Driver Warrick Couch John A. Peacock Ivan K. Baldry Carlton M. Baugh Joss Bland-Hawthorn Terry Bridges Russell Cannon Shaun Cole Chris Collins Nicholas Cross Gavin B. Dalton George Efstathiou Richard S. Ellis Carlos S. Frenk Karl Glazebrook Edward Hawkins Carole Jackson Ofer Lahav Ian Lewis Stuart Lumsden Steve Maddox Darren S. Madgwick Peder Norberg Will Percival Bruce Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2003,342(3):725-737
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39.
Chris Blake Michael B. Pracy Warrick J. Couch Kenji Bekki Ian Lewis Karl Glazebrook Ivan K. Baldry Carlton M. Baugh Joss Bland-Hawthorn Terry Bridges Russell Cannon Shaun Cole Matthew Colless Chris Collins Gavin Dalton Roberto De Propris Simon P. Driver George Efstathiou Richard S. Ellis Carlos S. Frenk Carole Jackson Ofer Lahav Stuart Lumsden Steve Maddox Darren Madgwick Peder Norberg John A. Peacock Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2004,355(3):713-727
40.
Will J. Percival Carlton M. Baugh Joss Bland-Hawthorn Terry Bridges Russell Cannon Shaun Cole Matthew Colless Chris Collins Warrick Couch Gavin Dalton Roberto De Propris Simon P. Driver George Efstathiou Richard S. Ellis Carlos S. Frenk Karl Glazebrook Carole Jackson Ofer Lahav Ian Lewis Stuart Lumsden Steve Maddox Stephen Moody Peder Norberg John A. Peacock Bruce A. Peterson Will Sutherland Keith Taylor 《Monthly notices of the Royal Astronomical Society》2001,327(4):1297-1306
The 2dF Galaxy Redshift Survey has now measured in excess of 160 000 galaxy redshifts. This paper presents the power spectrum of the galaxy distribution, calculated using a direct Fourier transform based technique. We argue that, within the k -space region , the shape of this spectrum should be close to that of the linear density perturbations convolved with the window function of the survey. This window function and its convolving effect on the power spectrum estimate are analysed in detail. By convolving model spectra, we are able to fit the power-spectrum data and provide a measure of the matter content of the Universe. Our results show that models containing baryon oscillations are mildly preferred over featureless power spectra. Analysis of the data yields 68 per cent confidence limits on the total matter density times the Hubble parameter , and the baryon fraction , assuming scale-invariant primordial fluctuations. 相似文献