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531.
Alessandro Bonaccorso Alessandro Bonforte Salvatore Gambino 《Bulletin of Volcanology》2010,72(7):791-801
Between 1987 and 1993, fumarole temperatures at the Fossa crater of Vulcano (Italy) were characterized by the highest values
since the 1920’s, increasing from about 300°C in 1987 to 690°C in May 1993, before decreasing to 400°C by 1996–1997. During
1990, Vulcano’s Electronic Distance Measurement (EDM) network was expanded to provide more detailed coverage of the northern
sector of the Fossa crater and, in particular, to monitor the movement of the northern flank the Fossa cone. Measurements,
carried out between 1990 and 1994, showed shortening by about 6 to 7 cm along baselines measured to a small section of the
northern rim. Over the following four years these baselines showed a slow extension by about 3 cm, to gradually recover part
of the previous deformation. We believe that the shortening and lengthening of the EDM baselines was respectively due to the
increasing and decreasing temperature of the rock body lying close to the deforming area. This caused thermal expansion, followed
by contraction. The positive movement of the rim was not completely matched by a negative recovery, suggesting that a non-recoverable
sliding movement was also responsible for some of the shortening of the baselines. We verified our hypothesis by calculating
the expected dilatation of a rock body, as a function of the volume of rock heated and its thermal expansion coefficient,
and compared the expected deformation to that observed. The geodetic investigation showed that the unstable portion affects
a small length of the rim (about 100 m long) and involves a volume of about 0.8 × 106 m3. However, this zone lies directly above a particularly unstable portion of the flank, as well as the main village and port
on the island. 相似文献
532.
Long‐term river meandering as a part of chaotic dynamics? A contribution from mathematical modelling
In the present contribution we focus our attention on the possible signatures of a chaotic behaviour or a self‐organized criticality state triggered in river meandering dynamics by repeated occurrence of cutoff processes. The analysis is carried out examining, through some robust nonlinear methodologies inferred from time series analysis, both the spatial series of local curvatures and the time series of long‐term channel sinuosity. Temporal distribution of cutoff inter‐arrivals is also investigated. The analyzed data have been obtained by using a suitable physics‐based simulation model for river meandering able to reproduce reasonably the features of real rivers. The results are consistent and show that, at least from a modelling point of view, no evidence of chaotic determinism or self‐organized criticality is detectable in the investigated meandering dynamics. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
533.
Investigation techniques for karst flow systems are based mainly on the study of different signals leaving the system caused by natural or induced external influences. Each signal represents one of the systems outputs (e.g., hydraulic, chemical, physical, or isotopic responses) that reflect the characteristics of the entire system. In this paper, we present a method to infer information about the structure of karst systems. It is based on a simultaneous analysis of chemical and hydraulic responses. Beside the classical piston flow at the beginning of a flood pulse, we define a chemically based recession flow phase. During this phase, field data show that the concentration of total dissolved solids can be considered as an exponential function of the logarithm of flow. This relationship allows two parameters to be defined, one of which is dependent on the structure and degree of development of the karst conduit network, the other is dependent mainly on bioclimatic factors. Data collected from seven karst springs are used to support ideas introduced in the paper. 相似文献
534.
We have developed a preliminary version of a new type of code to simulate the outcomes of impacts between solid bodies, which we plan to further refine for application to both asteroid science and space debris studies. In the current code, colliding objects are modeled as two-dimensional arrays of finite elements, which can interact with each other in both an elastic and a shock-wave regime. The finite elements are hard spheres with a given value for mass and radius. When two of them come into contact the laws of inelastic scattering are applied, thus giving rise to the propagation of shock waves. Moreover each spherical element interacts elastically with its nearest neighbours. The interaction force corresponds to that of a spring having an equilibrium length equal to the lattice spacing, and results into the propagation of elastic waves in the lattice. Dissipation effects are modeled by means of a dissipative force term proportional to the relative velocity, with a given characteristic time of decay. The possible occurrence of fractures in the material is modeled by assuming that when the distance of two neighbouring elements exceeds a threshold value, the binding force between them disappears for ever. This model requires finding a plausible correspondence between the input parameters appearing in the equations of motion, and the physical properties of real solid materials. Some of the required links are quite obvious (e.g., the relationship between mass of the elements and elastic constant on one side, and material density and sound velocity on the other side), some others a priori are unclear, and additional hypotheses on them must be made (e.g., on the restitution coefficient of inelastic scattering). Despite the preliminary character of the model, we have obtained some interesting results, which appear to mimic in a realistic way the outcomes of actual impacts. For instance, we have observed the formation of craters and fractures, and (for high impact energies) the occurrence of catastrophic breakup. The masses and velocities of the fragments resemble those found in laboratory impact experiments. 相似文献
535.
We describe the use of the magneto-optic filter (MOF) to observe solar magnetic fields in the potassium line at 7699 Å. The filter has been used in the Big Bear video-magnetograph since 23 October. It gives a high sensitivity and dynamic range for longitudinal magnetic fields and enables us to measure transverse magnetic fields using the sigma component. Examples of the observations are presented.This paper was presented at the third meeting of the Solar Cycle Workshop, held in Sydney, Australia, January 9–13, 1989.NRC Senior Res. Fellow. 相似文献
536.
Experimental and Numerical Studies on the Seismic Response of R.C. Hollow Bridge Piers 总被引:3,自引:2,他引:1
Gian?Michele?CalviEmail author Alberto?Pavese Alessandro?Rasulo Davide?Bolognini 《Bulletin of Earthquake Engineering》2005,3(3):267-297
Appropriate seismic assessment of reinforced concrete bridges is an important challenge in structural engineering in consideration
of the number and relevance of bridges built without applying advanced codes of practice and of the strategic role of transportation
networks in modern economy. This paper focuses on some relevant aspects of the damage development and collapse modes of hollow
piers, as commonly designed in the past. The following aspects have been considered: absence of confinement, inadequate shear
strength, shifting of the critical section, insufficient length of lap splices. A series of experimental tests has been designed
and performed; the capacity of predicting appropriate results of formulations recommended in codes of practice or proposed
in recent research documents has been checked comparing experimental and analytical results. 相似文献
537.
Alessandro Iannace Glauco Bonardi Marco D'Errico Stefano Mazzoli Vincenzo Perrone Stefano Vitale 《Comptes Rendus Geoscience》2005,337(16):373
A new structural–stratigraphic synthesis of the Apennine units of northern Calabria is presented. The Meso-Cenozoic successions are grouped into two tectonic units, named Pollino–Ciagola Unit (PCU) and Lungro–Verbicaro Unit (LVU), comprising terrains formerly attributed to five different tectonic units. FeMg carpholite and blue amphibole record HP–LT metamorphism in the LVU, followed by progressive decompression leading to final greenschist facies re-equilibration during dominantly extensional deformation. Final tectonic emplacement of the LVU over the PCU post-dated the metamorphism of the LVU and was accompanied by intense ductile deformation along zones of strain localisation in footwall rocks. All of the units were later affected by folding and minor thrusting during subsequent Apennine tectonics. To cite this article: A. Iannace et al., C. R. Geoscience 337 (2005). 相似文献
538.
A syn-eruptive ground deformation episode measured by GPS,during the 2001 eruption on the upper southern flank of Mt Etna 总被引:4,自引:0,他引:4
Alessandro?BonforteEmail author Francesco?Guglielmino Mimmo?Palano Giuseppe?Puglisi 《Bulletin of Volcanology》2004,66(4):336-341
Ground deformation occurring on the southern flank of Mt Etna volcano during the July–August 2001 eruption was monitored by GPS measurements along an E–W profile crossing the fissure system. This profile was measured eight times during the eruption, using the 'stop and go' semi-kinematic technique. Horizontal and vertical displacements between GPS surveys are reported for each station. The most significant event is a deformation episode occurring during the first week of the eruption, between 25–27 July. Displacements were measured on benchmarks close to the eruptive fissure and the tensile 1989 fracture. Data inversions for measured displacements were performed using the Okada model. The model shows the narrowing of the 2001 dyke accompanied by a dextral dislocation along an east-dipping fault, parallel to the 1989 fracture.Editorial responsibility: T. Druitt 相似文献
539.
A. A. Deshpande F. D’Alessandro P. M. McCulloch 《Journal of Astrophysics and Astronomy》1996,17(1-2):7-16
Spectral analysis of the residual pulsearrival times of pulsars is a useful tool in understanding the nature of the underlying
processes that may be responsible for the timing noise observed from pulsars. Power spectra of pulsar timing residuals may
be described by one or a combination of powerlaws. As these spectra are expected to be very steep, it is important to ensure
a high dynamic range in the estimation of the spectrum. This is difficult in practice since one is, in general, dealing with
timing measurements made at unevenly placed epochs. In this paper, we present a technique based on, ‘CLEAN’ to obtain high
dynamic range spectra from unevenly sampled data. We compare the performance of this technique with other techniques including
some that were used earlier for estimation of power spectra of pulsar timing residuals. 相似文献
540.
Massimilliano Guzzo Alessandro Morbidelli 《Celestial Mechanics and Dynamical Astronomy》1996,66(3):255-292
We investigate the possibility of obtaining a Nekhoroshev like result for the dynamical system describing the motion of an asteroid in the main belt, From the mathematical point of view this is a new result since the problem is degenerate and we want to control also the motion of degenerate actions, We find that there are regions, such as the resonances of low order among the fast angles (mean motion resonances), where a Nekhoroshev like result cannot be proved a priori, Conversely, we are able to confine the motions in the mean motion resonances of logarithmically large order in the perturbation parameters, as well as in the non-resonant region, We discuss also the connection with the existence of invariant tori. 相似文献