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101.
Sebastian Heinz Andrea Merloni Tiziana Di Matteo Rashid Sunyaev 《Astrophysics and Space Science》2005,300(1-3):15-21
The scale invariance model (Heinz, S. and Sunyaev, R.A.: 2003, MNRAS 343, L59) can be used to derive robust scaling relations between the radio luminosity from accreting black holes and the black
hole mass and accretion rate. These relations agree well with the recently found “fundamental plane” of black hole activity
(Merloni, A., Heinz, S. and Di Matteo, T.: 2003, MNRAS 345, 1057). This relation provides a new, powerful tool for the comparison of jets from black holes of different masses and accretion
rates. The regression coefficients of this relation contain information about the nature of the X-ray emission mechanism driving
the correlation. We argue that X-ray synchrotron emission from the base of the jets is unlikely to be the dominant contribution
to the X-ray spectrum in most of the sources. 相似文献
102.
103.
104.
John A. Regan Martin G. Haehnelt Matteo Viel 《Monthly notices of the Royal Astronomical Society》2007,374(1):196-205
We compare simulations of the Lyman α forest performed with two different hydrodynamical codes, gadget-2 and enzo . A comparison of the dark matter power spectrum for simulations run with identical initial conditions show differences of 1–3 per cent at the scales relevant for quantitative studies of the Lyman α forest. This allows a meaningful comparison of the effect of the different implementations of the hydrodynamic part of the two codes. Using the same cooling and heating algorithm in both codes, the differences in the temperature and the density probability distribution function are of the order of 10 per cent. The differences are comparable to the effects of box size and resolution on these statistics. When self-converged results for each code are taken into account, the differences in the flux power spectrum – the statistics most widely used for estimating the matter power spectrum and cosmological parameters from Lyman α forest data – are about 5 per cent. This is again comparable to the effects of box size and resolution. Numerical uncertainties due to a particular implementation of solving the hydrodynamic or gravitational equations appear therefore to contribute only moderately to the error budget in estimates of the flux power spectrum from numerical simulations. We further find that the differences in the flux power spectrum for enzo simulations run with and without adaptive mesh refinement are also of the order of 5 per cent or smaller. The latter require 10 times less CPU time making the CPU time requirement similar to that of a version of gadget-2 that is optimized for Lyman α forest simulations. 相似文献
105.
106.
Paolo Padovani Eric Perlman Hermine Landt Paolo Giommi Matteo Perri 《Astrophysics and Space Science》2004,294(1-2):71-78
We present a new population of radio quasars whose X-ray band, unlike previously known sources which have (flat) inverse Compton
radiation, is characterized by (steep) synchrotron emission, with a broad-band spectral energy distribution similar to that
of BL Lacs with high energy synchrotron peaks. We discuss how this new class was discovered, the class properties, and the
implications of its existence for our understanding of jets and active galactic nuclei in general. 相似文献
107.
Sebastiano Foti Stefano Parolai Dario Albarello Matteo Picozzi 《Surveys in Geophysics》2011,32(6):777-825
Surface-wave dispersion analysis is widely used in geophysics to infer a shear wave velocity model of the subsoil for a wide
variety of applications. A shear-wave velocity model is obtained from the solution of an inverse problem based on the surface
wave dispersive propagation in vertically heterogeneous media. The analysis can be based either on active source measurements
or on seismic noise recordings. This paper discusses the most typical choices for collection and interpretation of experimental
data, providing a state of the art on the different steps involved in surface wave surveys. In particular, the different strategies
for processing experimental data and to solve the inverse problem are presented, along with their advantages and disadvantages.
Also, some issues related to the characteristics of passive surface wave data and their use in H/V spectral ratio technique
are discussed as additional information to be used independently or in conjunction with dispersion analysis. Finally, some
recommendations for the use of surface wave methods are presented, while also outlining future trends in the research of this
topic. 相似文献
108.
Matteo Picozzi Claus Milkereit Kevin Fleming Eser Çakti Jochen Zschau 《Journal of Seismology》2011,15(4):557-578
A seismic antenna approach based on the generalized zero-lag cross-correlation method for rapid earthquake localization is
proposed. This method is intended to be applied primarily for early warning, whenever the epicentre-to-target distances guarantee
enough lead-time, rapid response purposes, and for those circumstances when a seismogenic area is not directly accessible
with seismic stations or/and a network of instruments is concentrated within the area to be warned. The procedure we propose
aims to provide useful information for magnitude determination and shake-maps generation. Indeed, it relies only on the first
P-wave triggered arrivals from seismic stations, and is designed to work in real-time for the localization of events occurring
outside of the network, that is, under conditions that might be detrimental to standard localization approaches. The procedure
can by summarized by a few preliminary pre-seismic and real-time co-seismic steps. In the pre-seismic time-frame, for the
cases where a large and dense network exists, waiting for all stations to trigger could dramatically reduce the available
lead-time for the warning. Therefore, in such cases, the network could profitably be divided into sub-arrays, while also taking
advantage of available earthquake recordings or simulated data sets. During the co-seismic time-frame, the main operations
are: (1) individual on-site triggering by the P-wave of the seismic stations (e.g. by a STA/LTA algorithm); (2) real-time
communication of key parameters (e.g. P-wave arrival time, and signal quality) to a main centre by SMS/WLAN; (3) setup of
a pseudo data set, composed by a Gaussian function centred at the P-time, and with a bell width that can be set up proportional
to the trigger signal-to-noise ratio (SNR); (4) calculation of a coherency map for the sub-array with triggered stations (preliminary
sub-array location); and (5) stacking of coherency maps from the different sub-arrays (final location). By the stack of coherency
maps estimated by the different sub-arrays in the last step of the procedure, the epicentral area’s location may be better
constrained. This innovative approach for rapid localization was applied to both synthetic data, and real observations of
two small earthquakes that occurred in the Marmara Sea, Turkey, which were recorded by the Istanbul Earthquake Rapid Response
System. 相似文献
109.
Marco Mucciarelli Marcello Bianca Rocco Ditommaso Marco Vona Maria Rosaria Gallipoli Alessandro Giocoli Sabatino Piscitelli Enzo Rizzo Matteo Picozzi 《Bulletin of Earthquake Engineering》2011,9(3):825-840
In San Gregorio (L’Aquila, Italy) a three-story, reinforced concrete (RC) building had the first floor collapsed following
the earthquake of April 6, 2009. The remaining two stories fell with a displacement in the horizontal projection of about
70 cm. This unusual behaviour is made more puzzling by the fact that buildings located at a short distance and with similar
features had little or no damage reported. To understand the causes of the collapse we performed strong motion recordings,
microtremor measurements, a detailed geological survey, a high-resolution geo-electrical tomography, a borehole with a down-hole
test. On the building we performed a geometrical survey and laboratory tests on concrete cores. The acceleration and noise
recordings have shown a high amplification with uphill-downhill direction. The geological survey has revealed the presence
of co-seismic fractures on stiff soils. Geo-electrical tomography has shown an unexpected, strong discontinuity just below
the building. Taking advantage of excavations in adjacent lots, we have highlighted rare cataclastic decimetric bands with
a very low resistance material incorporated in well-stratified calcarenites. The same soft material has been founded in the
borehole down to 17 m from ground level, showing a shear wave velocity that starts at 250 m/s, increases with depth and has
an abrupt transition in calcarenites at 1,150 m/s. The surface geophysical measurements in the vicinity of the site have not
shown similar situations, with flat HVSR curves as expected for a rock outcrop, except for a lateral extension of the soft
zone. The analysis on the quality of the building materials has yielded values higher than average for the age and type of
construction, and no special design or construction deficiencies have been observed. A strong, peculiar site effect thus appears
to be the most likely cause of the damage observed. 相似文献
110.
Carme Boix Gianluca Frijia Vicent Vicedo Josep M. Bernaus Matteo Di Lucia Mariano Parente Esmeralda Caus 《Cretaceous Research》2011,32(6):806-822
The Upper Cretaceous La Cova limestones (southern Pyrenees, Spain) host a rich and diverse larger foraminiferal fauna, which represents the first diversification of K-strategists after the mass extinction at the Cenomanian–Turonian boundary.The stratigraphic distribution of the main taxa of larger foraminifera defines two assemblages. The first assemblage is characterised by the first appearance of lacazinids (Pseudolacazina loeblichi) and meandropsinids (Eofallotia simplex), by the large agglutinated Montsechiana montsechiensis, and by several species of complex rotalids (Rotorbinella campaniola, Iberorotalia reicheli, Orbitokhatina wondersmitti and Calcarinella schaubi). The second assemblage is defined by the appearance of Lacazina pyrenaica, Palandrosina taxyae and Martiguesia cyclamminiformis.A late Coniacian-early Santonian age was so far accepted for the La Cova limestones, based on indirect correlation with deep-water facies bearing planktic foraminifers of the Dicarinella concavata zone. Strontium isotope stratigraphy, based on many samples of pristine biotic calcite of rudists and ostreids, indicates that the La Cova limestones span from the early Coniacian to the early-middle Santonian boundary. The first assemblage of larger foraminifera appears very close to the early-middle Coniacian boundary and reaches its full diversity by the middle Coniacian. The originations defining the second assemblage are dated as earliest Santonian: they represent important bioevents to define the Coniacian-Santonian boundary in the shallow-water facies of the South Pyrenean province.By means of the calibration of strontium isotope stratigraphy to the Geological Time Scale, the larger foraminiferal assemblages of the La Cova limestones can be correlated to the standard biozonal scheme of ammonites, planktonic foraminifers and calcareous nannoplankton. This correlation is a first step toward a larger foraminifera standard biozonation for Upper Cretaceous carbonate platform facies. 相似文献