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231.
FIRST RESULTS FROM VIRGO,THE EXPERIMENT FOR HELIOSEISMOLOGY AND SOLAR IRRADIANCE MONITORING ON SOHO 总被引:1,自引:0,他引:1
Fröhlich Claus Andersen Bo N. Appourchaux Thierry Berthomieu Gabrielle Crommelynck Dominique A. Domingo Vicente Fichot Alain Finsterle Wolfgang Gómez Maria F. Gough Douglas Jiménez Antonio Leifsen Torben Lombaerts Marc Pap Judit M. Provost Janine Roca Cortés Teodoro Romero José Roth Hansjörg Sekii Takashi Telljohann Udo Toutain Thierry Wehrli Christoph 《Solar physics》1997,170(1):1-25
First results from the VIRGO experiment (Variability of solar IRradiance and Gravity Oscillations) on the ESA/NASA Mission SOHO (Solar and Heliospheric Observatory) are reported. The observations started mid-January 1996 for the radiometers and sunphotometers and near the end of March for the luminosity oscillation imager. The performance of all the instruments is very good, and the time series of the first 4–6 months are evaluated in terms of solar irradiance variability, solar background noise characteristics and p-mode oscillations. The solar irradiance is modulated by the passage of active regions across the disk, but not all of the modulation is straightforwardly explained in terms of sunspot flux blocking and facular enhancement. Helioseismic inversions of the observed p-mode frequencies are more-or-less in agreement with the latest standard solar models. The comparison of VIRGO results with earlier ones shows evidence that magnetic activity plays a significant role in the dynamics of the oscillations beyond its modulation of the resonant frequencies. Moreover, by comparing the amplitudes of different components ofp -mode multiplets, each of which are influenced differently by spatial inhomogeneity, we have found that activity enhances excitation. 相似文献
232.
The formation of dust grains in steady state dust driven winds around oxygen-rich AGB stars has been investigated to clarify
the carrier of the observed 13μm feature. In the calculations not only homogeneous Al2O3 and silicate grains but also heterogeneous
grains consisting of an Al2O3 core and a silicate mantle are included simultaneously. The radiation transfer calculations
based on the results of condensation calculations demonstrate that the core-mantle grains consisting of an α-Al2O3 core and
a silicate mantle formed in the vicinity of the sonic point can produce a distinctive emission feature similar to the observed
13μm feature when the mass loss rate is less than 2 × 10-5M·/yr.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
233.
234.
235.
Takashi Hamana † 《Monthly notices of the Royal Astronomical Society》2001,326(1):326-332
Gravitational lensing causes a correlation between a population of foreground large-scale structures and the observed number density of the background distant galaxies as a consequence of the flux magnification and the lensing area distortion. This correlation has not been taken into account in calculations of the theoretical predictions of the cosmic shear statistics but may cause a systematic error in a cosmic shear measurement. We examine its impact on the cosmic shear statistics using the semi-analytic approach. We find that the lensing magnification has no practical influence on the cosmic shear variance. Exploring the possible shapes of the redshift distribution of source galaxies, we find that the relative amplitude of the effect on the convergence skewness is 3 per cent at most. 相似文献
236.
Fractal structure of spatial distribution of microfracturing in rock 总被引:10,自引:0,他引:10
237.
This paper focuses on the geometry modelling and numerical analysis of microstructures of geomaterials employing the concept of image‐based engineering. The novel modelling and analysis techniques with digital images are incorporated with the mathematical homogenization method to study the interaction between individual phases, each of whose shape and spatial distribution are irregular. Owing to the distinctive features of these computational techniques, the evaluation of homogenized properties for geomaterials provides the reliable information about the micro‐ or macroscopic mechanical behaviours for engineering practice. It is, naturally, inevitable that engineers' demands on safety and efficient design place emphasis on quantitative estimates for these values. Thus, calibration accompanied with actual measurements comes within the scope of this study so that these properties would be realistic and practical from the engineering viewpoints. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
238.
Takashi Yamamoto 《Planetary and Space Science》1976,24(11):1073-1080
Models of acceleration of auroral electrons by electrostatic shock waves are considered based on the model electron beam, calculated by Evans (1974), to account for the observed precipitating electron fluxes. Electron populations in our models include a primary accelerated beam, originating from the plasma sheet, the secondary electrons and the energy-degraded and backscattered primary electrons produced by precipitating electrons of that beam. We find a feasible electrostatic shock model with appropriate ion populations from considerations on the conditions for the existence of shock solutions. 相似文献
239.
Nina Daneu Aleksander Rečnik Takashi Yamazaki Tadej Dolenec 《Physics and Chemistry of Minerals》2007,34(4):233-247
The atomic scale structure and chemistry of (111) twins in MgAl2O4 spinel crystals from the Pinpyit locality near Mogok (Myanmar, formerly Burma) were analysed using complementary methods
of transmission electron microscopy (TEM). To obtain a three-dimensional information on the atomic structure, the twin boundaries
were investigated in crystallographic projections
and
Using conventional electron diffraction and high-resolution TEM (HRTEM) analysis we have shown that (111) twins in spinel
can be crystallographically described by 180° rotation of the oxygen sublattice normal to the twin composition plane. This
operation generates a local hcp stacking in otherwise ccp lattice and maintains a regular sequence of kagome and mixed layers. In addition to rotation, no other translations are present
in (111) twins in these spinel crystals. Chemical analysis of the twin boundary was performed by energy-dispersive X-ray spectroscopy
(EDS) using a variable beam diameter (VBD) technique, which is perfectly suited for analysing chemical composition of twin
boundaries on a sub-nm scale. The VBD/EDS measurements indicated that (111) twin boundary in spinel is Mg-deficient. Quantitative
analyses of HRTEM (phase contrast) and HAADF-STEM (Z-contrast) images of (111) twin boundary have confirmed that Mg2+ ions are replaced with Be2+ ions in boundary tetrahedral sites. The Be-rich twin boundary structure is closely related to BeAl2O4 (chrysoberyl) and BeMg3Al8O16 (taaffeite) group of intermediate polysomatic minerals. Based on these results, we conclude that the formation of (111) twins
in spinel is a preparatory stage of polytype/polysome formation (taaffeite) and is a result of thermodynamically favourable
formation of hcp stacking due to Be incorporation on the {111} planes of the spinel structure in the nucleation stage of crystal growth. The
twin structure grows as long as the surrounding geochemical conditions allow its formation. The incorporation of Be induces
a 2D-anisotropy and exaggerated growth of the crystal along the (111) twin boundary. 相似文献
240.
Twenty four solar bursts of peak fluxes above 50 sfu are analyzed which were observed with the 17 GHz interferometer at Nobeyama during the period from 1978 September to 1979 December. Source characteristics and their temporal evolutions are investigated on a statistical basis with high time resolutions up to 0.8 s. Use of a model-fitting technique recently developed by Kosugi (1982) is made to derive both the position of centroid and size (~ FWHM) of burst source with an uncertainty of a few arc sec. The results of this study are the following:
- Two different phases in the burst, that is to say, the main phase and the post-burst-increase (PBI) phase, are distinguished clearly not only by the morphological difference of flux time profile, but also by the differences of brightness temperature (107-?109 K vs 105–107 K), circular polarization degree (0–50% vs 0–10%), and size (?5–25″ vs 10–70″). There is no definite correlation between the peak fluxes in the two phases.
- The majority of the selected bursts (21 of 24) show in the main phase source characteristics of the impulsive burst. The total flux varies rapidly (characteristic time scale defined by FWHM ? 100 s), often associated with the rapid shift of position and the rapid change of polarization degree. The source height of the impulsive source is lower than that of the PBI source. On the other hand, the type IVμ source, seen in three events, shows a gradual variation and the source ascends to a height of ~ 40 000 km above the photosphere.
- In the PBI phase, the expansion and ascension of the source occur in general (21 of 23 for the former and 12 of 15 for the latter). The velocities of both the movements are of the order of 5 km s?1.