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91.
Ryosuke Sinmyo Elena Bykova Catherine McCammon Ilya Kupenko Vasily Potapkin Leonid Dubrovinsky 《Physics and Chemistry of Minerals》2014,41(6):409-417
Magnesium silicate perovskite is the predominant phase in the Earth’s lower mantle, and it is well known that incorporation of iron has a strong effect on its crystal structure and physical properties. To constrain the crystal chemistry of (Mg, Fe)SiO3 perovskite more accurately, we synthesized single crystals of Mg0.946(17)Fe0.056(12)Si0.997(16)O3 perovskite at 26 GPa and 2,073 K using a multianvil press and investigated its crystal structure, oxidation state and iron-site occupancy using single-crystal X-ray diffraction and energy-domain Synchrotron Mössbauer Source spectroscopy. Single-crystal refinements indicate that all iron (Fe2+ and Fe3+) substitutes on the A-site only, where \( {\text{Fe}}^{ 3+ } /\Upsigma {\text{Fe}}\sim 20\,\% \) based on Mössbauer spectroscopy. Charge balance likely occurs through a small number of cation vacancies on either the A- or the B-site. The octahedral tilt angle (Φ) calculated for our sample from the refined atomic coordinates is 20.3°, which is 2° higher than the value calculated from the unit-cell parameters (a = 4.7877 Å, b = 4.9480 Å, c = 6.915 Å) which assumes undistorted octahedra. A compilation of all available single-crystal data (atomic coordinates) for (Mg, Fe)(Si, Al)O3 perovskite from the literature shows a smooth increase of Φ with composition that is independent of the nature of cation substitution (e.g., \( {\text{Mg}}^{ 2+ } - {\text{Fe}}^{ 2+ } \) or \( {\text{Mg}}^{ 2+ } {\text{Si}}^{ 4+ } - {\text{Fe}}^{ 3+ } {\text{Al}}^{ 3+ } \) substitution mechanism), contrary to previous observations based on unit-cell parameter calculations. 相似文献
92.
93.
Leonid S. Lyubimkov Tamara M. Rachkovskaya Sergey I. Rostopchin David L. Lambert 《Monthly notices of the Royal Astronomical Society》2002,333(1):9-26
Effective temperatures T eff , surface gravities log g and interstellar extinctions A V are found for 107 B stars. Distances d of the stars, which are based on the derived T eff , log g and A V values, show good agreement with those obtained from the Hipparcos parallaxes. Comparing the T eff and log g values with evolutionary computations, we infer masses, radii, luminosities, ages and relative ages of the stars. Empirical relations between the T eff and log g parameters, on the one hand, and the photometric indices Q , [ c 1 ] and β , on the other hand, are constructed; these relations give a fast method for the T eff and log g estimation of early and medium B stars. Inclusion of the infrared J , H and K colours into the T eff , log g and A V determination shows that (i) the T eff and log g parameters are altered only slightly; (ii) the A V value is rather sensitive to these colours, so an accuracy better than 0.05 mag in the JHK data is necessary for precise A V evaluation. 相似文献
94.
Leonid S. Pilyugin José M. Vílchez Trinh X. Thuan 《Monthly notices of the Royal Astronomical Society》2006,370(4):1928-1934
We suggest a new way to establish the relation between the electron temperature t 3 within the [O iii ] zone and the electron temperature t 2 within the [O ii ] zone in high-metallicity (12 + log(O/H) > 8.25) H ii regions. The t 2 – t 3 diagram is constructed by applying our method to a sample of 372 H ii regions. We find that the correlation between t 2 and t 3 is tight and can be approximated by a linear expression. The new t 2 – t 3 relation can be used to determine t 2 and accurate abundances in high-metallicity H ii regions with a measured t 3 . It can also be used in conjunction with the ff relation for the determination of t 3 and t 2 and oxygen abundances in high-metallicity H ii regions, where the [O iii ]λ4363 auroral line is not detected. The derived t 2 – t 3 relation is independent of photoionization models of H ii regions. 相似文献
95.
A new natural,super-hard,transparent polymorph of carbon from the Popigai impact crater,Russia 总被引:1,自引:0,他引:1
Ahmed El Goresy Leonid S Dubrovinsky Philippe Gillet Smail Mostefaoui Günther Graup Michael Drakopoulos Alexandre S Simionovici Varghese Swamy Victor L Masaitis 《Comptes Rendus Geoscience》2003,335(12):889-898
A natural shockwave event led to the formation of a new crystalline polymorph of carbon in gneisses from the Popigai crater, Russia. The new species occupies the interior of a multiphase assemblage and is entirely enveloped by lonsdaleite and graphite. Polishing hardness of this new phase is greater than that of lonsdaleite. Micro-beam synchrotron X-ray diffraction, imaging and fluorescence studies revealed a pure transparent carbon phase. The diffraction pattern is indexed in terms of a cubic cell (a=14.697 Å, space group Pm3m.). This species was neither encountered in static or dynamic high-pressure experiment nor predicted by theoretical calculations. To cite this article: A. El Goresy et al., C. R. Geoscience 335 (2003). 相似文献
96.
97.
Olga N. Karasyova Lyudmila I. Ivanova Leonid Z. Lakshtanov Lars Lövgren Staffan Sjöberg 《Aquatic Geochemistry》1998,4(2):215-231
The acid/base properties of the hematite/water interface and surfacecomplexation with gold has been studied by potentiometric titrations in thefour component system H+ – FeOH –AuCl
4
-
– Cl-. Equilibrium measurementswere performed in NaCl media at 298.2 K. In the evaluation of equilibriummodel from experimental data the constant capacitance model was applied. Theacid/base properties were investigated in 0.1 M NaCl in the range 2.6 pH 7.4. The resulting intrinsic constants for protonation anddeprotonation of hydroxyl groups at the surface were log
1,1,0,0(int)
s
= 7.10 ± 0.06 andlog
-1,1,0,0(int)
s
= - 7.80 ±0.06. The density of proton active surface sites was 2.85nm-2 and the specific capacitance 2.5 C V-1 m-2. In the investigation of surface complexation of gold, thepotentiometric titrations were performed in the range 2.0 pH 10.2.Titration data was supplemented with analysis of Au in the aqueous phase byatomic absorbance spectrometry. The equilibrium model proposed consists ofthe following monodentate surface complexes: FeOHAuCl3(log
0,1,1,-1
s
= 1.45 ± 0.03),FeOHAuCl2OH (log
-1,1,1,-2
s
= -3.89 ± 0.02), FeOHAu(OH)3 (log
-3,1,1,-4
s
= -21.94 ± 0.05). Aslightly better fit could be obtained by assuming formation of a bidentatecomplex with the composition(FeO)2Au(OH)H2O. However, based onstructural arguments this complex was rejected. 相似文献
98.
High-pressure and high-temperature in situ X-ray diffraction study of iron and corundum to 68 GPa using an internally heated diamond anvil cell 总被引:1,自引:1,他引:0
Leonid S. Dubrovinsky Surendra K. Saxena Peter Lazor 《Physics and Chemistry of Minerals》1998,25(6):434-441
Using powder X-ray diffraction of heated solids to pressures reaching 68 GPa, the pressure-volume-temperature (PVT) data on
corundum Al2O3 and ɛ-Fe were determined with the following results:
*Corundum,*Iron, *Al2O3*ɛ-Fe
Isothermal bulk*258 (2)*164 (3) modulus K'300, 1 (GPa)
Pressure derivative K300, 1*4.88 (4)*5.36 (16)
Temperature derivative*–0.020 (2)*–0.043 (3) (∂K
T,1
/∂T)
P
(GPa/K)
Molar volume V300,1*25.59 (2)*6.76 (2) (cm3/mol)
Isobaric thermal expansion at 1 atm (0.101 MPa) is given by (K–1):
α
T
=2.6 (2) 10–5+1.81 (9) 10–9
T–0.67 (6)/T
2 for corundum, and α
T
=5.7 (4) 10–5+4.2 (4) 10–9
T–0.17 (7)/T
2 for iron ɛ-Fe.
Received: 1 March 1997 / Revised, accepted: 21 August 1997 相似文献
99.
Michael S. Zhdanov Vjacheslav V. Spichak Leonid Yu. Zaslavsky 《Physics of the Earth and Planetary Interiors》1990,60(1-4):53-61
A method for numerical modeling of quasi-stationary electromagnetic fields in axially symmetric media is proposed. It is based on the direct finite-element method and the use of special basis functions. Assuming cylindrical coordinates r, φ, z, the three-dimensional solution is presented as a superposition of fields with the azimuthal dependence exp(inφ). For each case this results in a system of two equations of elliptical type in two scalar functions in the (r, z) plane.
The discretization leads to the conservative nine-points difference scheme. The system of linear equations is solved by means of the LU-decomposition technique, the band structure of the matrix being taken into account.
The program is tested using analytical results (DC asymptote) for a near-surface inhomogeneity. Comparison also is made with 2D results (H-polarization) for the model of a local well conducting inclusion in a three-layered Earth. 相似文献
100.