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941.
The new Antarctic TALDICE ice core (72° 49′ S, 159° 11′ E, 1620 m depth), containing abundant primary tephras, provides the opportunity to elucidate the late Quaternary volcanic history of the south polar region, as well as to broaden the East Antarctic tephrostratigraphic framework. Here grain size and glass compositional data for representative tephra layers from the last 70 ka core section are used for source identification. Results point to origin of layers from centres of the Melbourne Volcanic Province (McMurdo Volcanic Group), located ~250 km from the coring site. Occurrence of tephra layers within the ice core record suggests that explosive activity in the identified source was not constant over the considered period, with a minimum of activity between 20 and 35 ka, and increased activity back to 65 ka. In addition to palaeovolcanic implications, the TALDICE tephra layers offer prospects for firm correlations between diverse widely separated palaeoarchives and for accurate dating of the Antarctic climatic record. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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944.
Falko Langenhorst Jean‐Paul POIRIER Alexander DEUTSCH Ulrich HORNEMANN 《Meteoritics & planetary science》2002,37(11):1541-1553
Abstract— A shock experiment has been devised to produce large shear in a single crystal sample of olivine. The recovered sample exhibits macroscopic shear faults resembling shock veins in ordinary chondrites. Examination with transmission electron microscopy reveals a high density of dislocations in the bulk olivine. The shear faults appear as thin veins containing small grains of olivine and pockets of glass. The microstructure and composition of the material in the veins point to fractional crystallization of a melt. An order of magnitude calculation is consistent with the idea that the veins were produced by shear melting. These results support the view that shock veins in meteorites are the result of shear heating rather than of pressure heterogeneities. 相似文献
945.
The first cosmic mirage was discovered approximately 20 years ago as the double optical counterpart of a radio source. This
phenomenon had been predicted some 70 years earlier as a consequence of General Relativity. We present here a summary of what
we have learnt since. The applications are so numerous that we had to concentrate on a few selected aspects of this new field
of research.
This review is focused on strong gravitational lensing, i.e. the formation of multiple images, in QSO samples. It is intended
to give the reader an up-to-date status of the observations and to present an overview of its most interesting potential applications
in cosmology and astrophysics, as well as numerous important results achieved so far.
The first section follows an intuitive approach to the basics of gravitational lensing and is developed in view of our interest
in multiply imaged quasars. The astrophysical and cosmological applications of gravitational lensing are outlined in Sect.
2 and the most important results are presented in Sect. 5. Sections 3 and 4 are devoted to the observations. Finally, conclusions
are summarized in the last section.
We have tried to avoid duplication with existing (and excellent) introductions to the field of gravitational lensing. For
this reason, we did not concentrate on the individual properties of specific lens models, as these are already well presented
in Narayan and Bartelmann (1996) and on a more intuitive ground in Refsdal and Surdej (1994). Wambsganss (1998) proposes a
broad view on gravitational lensing in astronomy; the reviews by Fort and Mellier (1994) and Hattori et al. (1999) deal with
lensing by galaxy clusters; microlensing in the Galaxy and the local group is reviewed by Paczyński (1996) and a general panorama
on weak lensing is given by Bartelmann and Schneider (1999) and Mellier (1999). The monograph on the theory of gravitational
lensing by Schneider, Ehlers and Falco (1992) also remains a reference in the field.
Received 4 April 2000 / Published online 9 August 2000 相似文献
946.
Duncan A. Forbes Antonis E. Georgakakis Jean P. Brodie 《Monthly notices of the Royal Astronomical Society》2001,325(4):1431-1440
The presence of two globular cluster subpopulations in early-type galaxies is now the norm rather than the exception. Here we present two more examples for which the host galaxy appears to have undergone a recent merger. Using multi-colour Keck imaging of NGC 1052 and 7332 we find evidence for a bimodal globular cluster colour distribution in both galaxies, with roughly equal numbers of blue and red globular clusters. The blue ones have similar colours to those in the Milky Way halo and are thus probably very old and metal-poor. If the red globular cluster subpopulations are at least of solar metallicity, then stellar population models indicate young ages. We discuss the origin of globular clusters within the framework of formation models. We conclude that recent merger events in these two galaxies have had little effect on their overall globular cluster systems. We also derive globular cluster density profiles, global specific frequencies and, in the case of NGC 1052, radial colour gradients and azimuthal distribution. In general these globular cluster properties are normal for early-type galaxies. 相似文献
947.
Alaa I. Ibrahim William C. Parke Jean H. Swank Hisham Anwer Roberto Turolla Silvia Zane M. T. Hussein T. El-Sherbini 《Astrophysics and Space Science》2007,308(1-4):43-50
The defining property of Soft Gamma Repeaters is the emission of short, bright bursts of X-rays and soft γ-rays. Here we present the continuum and line spectral properties of a large sample of bursts from SGR 1806-20, observed with
the Proportional Counter Array (PCA) onboard the Rossi X-ray Timing Explorer (RXTE). Using 10 trail spectral models (5 single
and 5 two component models), we find that the burst continua are best fitted by the single component models: cutoff power-law,
optically thin bremsstrahlung, and simple power-law. Time resolved spectroscopy show that there are two absorption lines at
∼5 keV and 20 keV in some bursts. The lines are relatively narrow with 90% upper limit on the line widths of 0.5–1.5 keV for
the 5 keV feature and 1–3 keV for the 20 keV feature. Both lines have considerable equivalent width of 330–850 eV for the
5 keV feature and 780–2590 eV for the 20 keV feature. We examined whether theses spectral lines are dependent upon the choice
of a particular continuum model and find no such dependence. Besides, we find that the 5 keV feature is pronounced with high
confidence in the cumulative joint spectrum of the entire burst sample, both in the individual detectors of the PCA and in
the co-added detectors spectrum. We confront the features against possible instrumental effects and find that none can account
for the observed line properties. The two features do not seem to be connected to the same physical mechanism because (1)
they do not always occur simultaneously, (2) while the 5 keV feature occurs at about the same energy, the 20 keV line centroid
varies significantly from burst to burst over the range 18–22 keV, and (3) the centroid of the lines shows anti-correlated
red/blue shifts. The transient appearance of the features in the individual bursts and in portions of the same burst, together
with the spectral evolution seen in some bursts point to a complex emission mechanism that requires further investigation.
相似文献
948.
Guillaume Bonello Jean Pierre Bibring Alain Soufflot Yves Langevin Brigitte Gondet Michel Berthé Charles Carabetian 《Planetary and Space Science》2005,53(7):711-728
Hyperspectral imagery is an essential technique for remote sensing of surfaces and atmospheres of planetary objects. However, given the instrumental complexity of coupling imaging and spectroscopy, in particular in the infrared, an in-depth ground calibration is mandatory to enable an unbiased and optimized data reduction.This paper presents the ground calibration setup designed and implemented for the visible and near infrared imaging spectrometers VIRTIS/ROSETTA, and OMEGA/MARS-EXPRESS, and summarizes the main results obtained in validating the required performances. 相似文献
949.
Christian Sue Bastien Delacou Jean‐Daniel Champagnac Cecile Allanic Martin Burkhard 《地学学报》2007,19(3):182-188
Neotectonics of the Western and Central Alps is characterized by ongoing widespread extension in the highest zones of the chain and transcurrent/compressive tectonics at the external limits of the belt. The overall geodetically measured deformations also indicate extension across the Western Alps. There is a good qualitative coherency between seismotectonic and geodetic approaches. Here we attempt to quantify the seismic part of the deformation. The seismic strain is compared to the deformation derived from geodesy. In sub‐areas of homogeneous seismic stress/strain, we computed the total seismic moment tensor and related strain tensor. This study provides new quantitative elements about the ongoing geodynamic processes in the alpine belt. The important discrepancies obtained between seismic strains and geodetically‐measured deformations raise the issue of aseismic deformation in the Alps, which could be related to elastic loading, creeping and/or a slower ductile‐style deformation. 相似文献
950.
We propose an analytic model that allows rapid computation of the secondary ion production due to electron impact from the primary photo-production in the ionosphere of Titan. The model parameters are given for each of the 5 major ion productions (N+2, CH+4, N+, CH+3, N++2) as well as for the electron production. 相似文献