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61.
The geoacoustic parameters form significant input for underwater acoustic propagation studies and geoacoustic modeling. Conventional
inversion techniques commonly used as indirect approach for extraction of geoacoustic parameters from acoustic or seismic
data are computationally intensive and time-consuming. In the present study, we have tried to exploit the advantage of soft
computing techniques like, reasoning ability of fuzzy logic and learning abilities of neural networks, in inversion studies.
The network model based on the combined approach called adaptive neuro-fuzzy inference system (ANFIS), is found to be very
promising in inversion of the acoustic data. The network model once built is capable of invert a few thousand data sets instantaneously,
to a reasonably good accuracy. In the case of conventional approaches, repetition of the entire inversion process with each
new data set is required. A limited number of sensor’s data are sufficient for simulation of the network model and provides
an advantage to use short hydrophone array data. Inversion results of a few hundred test data sets, representing different
geoacoustic environments, show the prediction error is much less than 0.01 g/cc, 10 m/s, 10 m and 0.1 against first layer’s
density, compressional sound speed, thickness and attenuation respectively for a three-layer geoacoustic model. However, the
error is relatively large for the second- and third-layer parameters, which need to be improved. The model is efficient, robust
and inexpensive. 相似文献
62.
Nonlinearity and complexity in gravel bed dynamics 总被引:1,自引:1,他引:0
Arvind Singh Stefano Lanzoni Efi Foufoula-Georgiou 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(7):967-975
The dynamics of river bed evolution are known to be notoriously complex affected by near-bed turbulence, the collective motion
of clusters of particles of different sizes, and the formation of bedforms and other large-scale features. In this paper,
we present the results of a study aiming to quantify the inherent nonlinearity and complexity in gravel bed dynamics. The
data analyzed are bed elevation fluctuations collected via submersible sonar transducers at 0.1 Hz frequency in two different
settings of low and high discharge in a controlled laboratory experiment. We employed surrogate series analysis and the transportation
distance metric in the phase-space to test for nonlinearity and the finite size Lyapunov exponent (FSLE) methodology to test
for complexity. Our analysis documents linearity and underlying dynamics similar to that of deterministic diffusion for bed
elevations at low discharge conditions. These dynamics transit to a pronounced nonlinearity and more complexity for high discharge,
akin to that of a multiplicative cascading process used to characterize fully developed turbulence. Knowing the degree of
nonlinearity and complexity in the temporal dynamics of bed elevation fluctuations can provide insight into model formulation
and also into the feedbacks between near-bed turbulence, sediment transport and bedform development. 相似文献
63.
Swami Saran Surendra Kumar K.G. Garg Arvind Kumar 《Geotechnical and Geological Engineering》2007,25(1):123-137
In the present paper, a method of analysis for calculating the pressure intensity corresponding to a given settlement for
eccentrically and obliquely loaded square and rectangular footings resting on reinforced soil foundation has been presented.
The process has been simplified by presenting non-dimensional charts for the various terms used in the analysis, which can
be directly used by practicing engineers. An approximate method has been suggested to find out the ultimate bearing capacity
of such footings on reinforced soil. The results have been validated with the model test results. The procedure has been made
clear by giving an illustrative example. 相似文献
64.
Arvind Bhatnagar 《Astrophysics and Space Science》1996,243(1):105-112
In this paper we present observations of two types of solar mass ejections, which seem to be associated with the location of coronal, holes. In the first type, a filament eruption was observed near a coronal hole, which gave rise to a strong interplanetary scintillations. as detected by IPS observations. In the second type, several large scale soft X-ray blow-outs were observed in the YOHKOH SXT X-ray movies, in all the cases they erupted from or near the boundary of coronal holes and over the magnetic neutral line. It is proposed that the open magnetic field configuration of the coronal hole provides, the necessary field structure for reconnection to take place, which in turn is responsible for filament eruption, from relatively lower heights. While, in the case of X-ray blow-outs, the reconnection takes place at a greater height, resulting in high temperature soft X-ray emission visible as X-ray blow-outs. 相似文献
65.
In the present paper we have studied the eigenfrequencies of small adiabatic barotropic pseudo-radial and nonradial modes of oscillations of the white dwarf models of rotating stars in binary systems. In this work the methodology of Mohan and Saxena (in Astrophys. Space Sci. 113:155, 1985) has been used that utilizes the averaging technique of Kippenhahn and Thomas (in Proc. IAU Colloq., vol. 4, p. 20, 1970) and certain results on Roche equipotential as that given by Kopal (in Advances in Astronomy and Astrophysics, Academic Press, 1972). The objective of this study is to investigate the effects of rotation and/or tidal distortion on the periods of oscillations of rotationally and/or tidally distorted white dwarf models of stars assuming it to be the primary component of the binary system and rotating uniformly. The results of present study show that the eigenfrequencies (both radial and nonradial modes) of the rotationally distorted and rotationally and tidally distorted white dwarf model of stars in binary systems tend to decrease under the influence of rotational distortions and rotational and tidal distortions, respectively. However, results are contrary for tidally distorted white dwarf model of stars. 相似文献