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951.
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
952.
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
953.
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
954.
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
955.
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
956.
Jeremie Vaubaillon Pavel Koten Anastasios Margonis Juraj Toth Regina Rudawska Maria Gritsevich Joe Zender Jonathan McAuliffe Pierre-Dominique Pautet Peter Jenniskens Detlef Koschny Francois Colas Sylvain Bouley Lucie Maquet Arnaud Leroy Jean Lecacheux Jiri Borovicka Junichi Watanabe Jürgen Oberst 《Earth, Moon, and Planets》2015,114(3-4):137-157
957.
958.
Guneshwar Thangjam Andreas Nathues Kurt Mengel Martin Hoffmann Michael Schäfer Vishnu Reddy Edward A. Cloutis Ulrich Christensen Holger Sierks Lucille Le Corre Jean‐Baptiste Vincent Christopher T. Russell 《Meteoritics & planetary science》2014,49(10):1831-1850
We present an analysis of olivine‐rich exposures at Bellicia and Arruntia craters using Dawn Framing Camera (FC) color data. Our results confirm the existence of olivine‐rich materials at these localities as described by Ammannito et al. ( 2013a ) using Visual Infrared Spectrometer (VIR) data. Analyzing laboratory spectra of various howardite–eucrite–diogenite meteorites, high‐Ca pyroxenes, olivines, and olivine‐orthopyroxene mixtures, we derive three FC spectral band parameters that are indicators of olivine‐rich materials. Combining the three band parameters allows us, for the first time, to reliably identify sites showing modal olivine contents >40%. The olivine‐rich exposures at Bellicia and Arruntia are mapped using higher spatial resolution FC data. The exposures are located on the slopes of outer/inner crater walls, on the floor of Arruntia, in the ejecta, as well as in nearby fresh small impact craters. The spatial extent of the exposures ranges from a few hundred meters to few kilometers. The olivine‐rich exposures are in accordance with both the magma ocean and the serial magmatism model (e.g., Righter and Drake 1997 ; Yamaguchi et al. 1997 ). However, it remains unsolved why the olivine‐rich materials are mainly concentrated in the northern hemisphere (approximately 36–42°N, 46–74°E) and are almost absent in the Rheasilvia basin. 相似文献
959.
A thermodynamically consistent extension of the constitutive equations of saturated soils to unsaturated conditions is often worked out through the use of a unique ‘effective’ interstitial pressure, accounting equivalently for the pressures of the saturating fluids acting separately on the internal solid walls of the pore network. The natural candidate for this effective interstitial pressure is the space averaged interstitial pressure. In contrast experimental observations have revealed that, at least, a pair of stress state variables was needed for a suitable framework to describe stress–strain–strength behaviour of unsaturated soils. The thermodynamics analysis presented here shows that the most general approach to the behaviour of unsaturated soils actually requires three stress state variables: the suction, which is required to describe the invasion of the soil by the liquid water phase through the retention curve; two effective stresses, which are required to describe the soil deformation at water saturation held constant. However a simple assumption related to the plastic flow rule leads to the final need of only a Bishop-like effective stress to formulate the stress–strain constitutive equation describing the soil deformation, while the retention properties still involve the suction and possibly the deformation. Commonly accepted models for unsaturated soils, that is the Barcelona Basic Model and any approach based on the use of an effective averaged interstitial pressure, appear as special extreme cases of the thermodynamic formulation proposed here. 相似文献
960.
Thomas Condom Anne Coudrain Jean Emmanuel Sicart Sylvain Thry 《Global and Planetary Change》2007,59(1-4):189
A previous study of Fox [Fox, A.N. 1993. Snowline altitude and climate at present and during the Last Pleistocene Glacial Maximum in the Central Andes (5°–28°S). Ph.D. Thesis. Cornell University.] showed that for a fixed 0 °C isotherm altitude, the equilibrium-line altitude (ELA) of the Peruvian and Bolivian glaciers from 5 to 20°S can be expressed based on a log–normal expression of local mid-annual rainfall amount (P). In order to extrapolate the function to the whole Andes (10°N to 55°S) a local 0 °C isotherm altitude is introduced. Two applications of this generalised function are presented. One concerns the space evolution of mean inter-annual ELA for three decades (1961–1990) over the whole South American continent. A high-resolution data set (grid data: 10′ for latitude/longitude) of mean monthly air surface temperature and precipitation is used. Mean annual values over the 1961–1990 period were calculated. On each grid element, the mean annual 0 °C isotherm altitude is determined from an altitudinal temperature gradient and mean annual temperature (T) at ground level. The 0 °C isotherm altitude is then associated with the annual precipitation amount to compute the ELA. Using computed ELA and the digital terrain elevation model GTOPO30, we determine the extent of the glacierised area in Andean regions under modern climatic conditions. The other application concerns the ELA time evolution on Zongo Glacier (Bolivia), where inter-annual ELA variations are computed from 1995 to 1999. For both applications, the computed values of ELA are in good agreement with those derived from glacier mass balance measurements. 相似文献