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71.
The shape parameter helps determining the shape of equilibrium beach profile in terms of offshore distance and water depth. The shape parameter therefore, should represent the effect of all the environmental factors involved in beach profile formation, such as wave climate and sediment properties. However, all the previous studies carried out to define shape parameter only consider the effects of sediment characteristics in their definitions. The aim of this study is to add the effect of wave climate also in the definition of shape parameter. This is achieved by integrating wave energy dissipation rate per unit volume at the surf zone. The result yields equilibrium wave energy dissipation rate that leads to theoretical definition of equilibrium beach profiles involving the effects of both the grain size and the wave climate parameters. It is found that the sediment grain size and the incoming wave height affect the value of shape parameter; whereas, the effects of wave period can be neglected. By means of energy equation, it is also possible to observe in macro scale the strength of wave energy on beach profile for different grain sizes. The findings also bring about the possibility of defining shape parameter such that any two arbitrary beach profiles owning the same sediment grain sizes can have the opportunity to have different beach profile formations. Finally, by adding the effect of wave height in the definition of shape parameter the graphical representation of the parameter, previously given by Moore (1982) is improved herein. 相似文献
72.
Michael J. Friedel 《Natural Hazards》2008,46(1):15-34
A regularized joint inverse procedure is presented and used to estimate the magnitude of extreme rainfall events in ungauged
coastal river basins of El Salvador: Paz, Jiboa, Grande de San Miguel, and Goascoran. Since streamflow measurements reflect
temporal and spatial rainfall information, peak-flow discharge is hypothesized to represent a similarity measure suitable
for regionalization. To test this hypothesis, peak-flow discharge values determined from streamflow recurrence information
(10-year, 25-year, and 100-year) collected outside the study basins are used to develop regional (country-wide) regression
equations. Peak-flow discharge derived from these equations together with preferred spatial parameter relations as soft prior
information are used to constrain the simultaneous calibration of 20 tributary basin models. The nonlinear range of uncertainty
in estimated parameter values (1 curve number and 3 recurrent rainfall amounts for each model) is determined using an inverse
calibration-constrained Monte Carlo approach. Cumulative probability distributions for rainfall amounts indicate differences
among basins for a given return period and an increase in magnitude and range among basins with increasing return interval.
Comparison of the estimated median rainfall amounts for all return periods were reasonable but larger (3.2–26%) than rainfall
estimates computed using the frequency-duration (traditional) approach and individual rain gauge data. The observed 25-year
recurrence rainfall amount at La Hachadura in the Paz River basin during Hurricane Mitch (1998) is similar in value to, but
outside and slightly less than, the estimated rainfall confidence limits. The similarity in joint inverse and traditionally
computed rainfall events, however, suggests that the rainfall observation may likely be due to under-catch and not model bias. 相似文献
73.
在对NiTi形状记忆合金(SMA)的力学性能试验研究的基础上,设计了一种新型SMA阻尼器,根据形状记忆合金丝的超弹性分段线性恢复力模型建立了阻尼器的理论模型,并通过阻尼器的性能试验研究验证了理论模型的正确性,试验结果表明这种阻尼器具有较好的耗能能力。 相似文献
74.
Bayesian stochastic modelling for avalanche predetermination: from a general system framework to return period computations 总被引:1,自引:1,他引:0
N. Eckert E. Parent M. Naaim D. Richard 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(2):185-206
Stochastic models are recent but unavoidable tools for snow avalanche hazard mapping that can be described in a general system
framework. For the computation of design return periods, magnitude and frequency have to be evaluated. The magnitude model
consists of a set of physical equations for avalanche propagation associated with a statistical formalism adapted to the input–output
data structure. The friction law includes at least one latent friction coefficient. The Bayesian paradigm and the associated
simulation techniques assist considerably in performing the inference and taking estimation errors into account for prediction.
Starting from the general case, simplifying hypotheses allows computing the predictive distribution of high return periods
on a case-study. Only release and runout altitudes are considered so that the model can use the French database. An inversible
propagation model makes it possible to work with the latent friction coefficient as if it is observed. Prior knowledge is
borrowed from an avalanche path with similar topographical characteristics. Justifications for the working hypotheses and
further developments are discussed. In particular, the whole approach is positioned with respect to both deterministic and
stochastic hydrology. 相似文献
75.
Since permanent wave-induced vibrations of offshore jacket platforms reduce the service life of the jacket structure and deck equipment and increase the fatigue failure of the welded connections, this research has used SMA (shape memory alloy) dampers to control the jacket platform oscillations. Superelasticity, high durability, and energy dissipation capability make SMA elements good nominees for the design of vibration control devices. In this research, to model the force-displacement hysteretic behavior of SMA elements their idealized multi-linear constitutive model has been implemented and the time history responses of vibration equations have been evaluated by direct integration method. To analyze the SMA damper effects on the vibration suppression of the jacket platforms, a 90 (m) high jacket located 80 (m) deep in water has been selected as a case study. Numerical results have shown that optimized SMA dampers with constant-geometry SMA bars will improve the dynamic behavior of the jacket platform under the action of an extreme regular wave. However, under the action of two irregular waves, SMA dampers with varying-geometry SMA bars will cause significant reduction in the dynamic responses of the jacket platform. The power spectral density function of the deck displacements have shown that the previously mentioned SMA dampers avoid resonance by shifting the natural frequencies of the jacket structure away from the excitation frequencies. 相似文献
76.
A precise value of the matrix-fracture transfer shape factor is essential for modeling fluid flow in fractured porous media by a dual-porosity approach. The slightly compressible fluid shape factor has been widely investigated in the literature. In a recent study, we have developed a transfer function for flow of a compressible fluid using a constant fracture pressure boundary condition [Ranjbar E, Hassanzadeh H, Matrix-fracture transfer shape factor for modeling flow of a compressible fluid in dual-porosity media. Adv Water Res 2011;34(5):627-39. doi:10.1016/j.advwatres.2011.02.012]. However, for a compressible fluid, the consequence of a pressure depletion boundary condition on the shape factor has not been investigated in the previous studies. The main purpose of this paper is, therefore, to investigate the effect of the fracture pressure depletion regime on the shape factor for single-phase flow of a compressible fluid. In the current study, a model for evaluation of the shape factor is derived using solutions of a nonlinear diffusivity equation subject to different pressure depletion regimes. A combination of the heat integral method, the method of moments and Duhamel’s theorem is used to solve this nonlinear equation. The developed solution is validated by fine-grid numerical simulations. The presented model can recover the shape factor of slightly compressible fluids reported in the literature. This study demonstrates that in the case of a single-phase flow of compressible fluid, the shape factor is a function of the imposed boundary condition in the fracture and its variability with time. It is shown that such dependence can be described by an exponentially declining fracture pressure with different decline exponents. These findings improve our understanding of fluid flow in fractured porous media. 相似文献
77.
Samuel Mansino Francisco Javier Ruiz-Sánchez Matthijs Freudenthal Plinio Montoya 《Proceedings of the Geologists' Association. Geologists' Association》2014
The species of the genus Apocricetus are considered to form the phyletic lineage A. aff. plinii (MN11)–A. plinii–A. alberti–A. barrierei–A. angustidens (MN16). Along this lineage, gradual morphological and biometrical changes occur, but not all the species are represented by rich populations. The assemblage of Apocricetus alberti from Venta del Moro is by far the most abundant collection of this species. This population shows a great morphological variability in some characters like the morphology of the anteroconid and the anterolophulids in m1 and the shape of the anterolophule in M1, with morphotypes that resemble both older and younger populations of Apocricetus. Along the phyletic lineage of Apocricetus, a change in the shape of m3 occurs, from predominantly subtriangular forms in the oldest populations to predominantly subrectangular in the youngest. To quantify this feature we use the posterior width of the molar and the anterior width/posterior width ratio, proposing five morphological categories, from extremely triangular to subrectangular. 相似文献
78.
The 1991–1993 lava flow is the most voluminous flow erupted at Mount Etna, Sicily, in over 300 years. Estimates of the volume
obtained by various methods range from 205×106 m3 (Tanguy 1996) to over 500×106 m3 (Barberi et al. 1993). This paper describes the results of an electronic distance measurement (EDM)-based field survey of
the upper surface of the 1991–1993 flow field undertaken in 1995. The results were digitised, interpolated and converted into
a digital elevation model and then compared with a pre-eruption digital elevation model, constructed from a 1 : 25 000 contour
map of the area, based on 1989 aerial photographs. Our measurements are the most accurate to date and show that the 1991–1993
lava flow occupies a volume of 231±29×106 m3.
Received: 20 July 1996 / Accepted: 5 November 1996 相似文献
79.
潮汐形变短临异常图像及其时空特征 总被引:3,自引:0,他引:3
展示了潮汐形变观测记录到的12个震例31个异常图像,总结了震例异常的特点、形态、量级,分析了潮汐形变波异常的时空特征:主震震级MS≥5.9级时出现异常的可能性大,异常出现的时间多为震前0.1~6.5天,MS为5、6、7、≥7.9时,异常的有效监测距离分别为70、300、500、2000km。 相似文献
80.
Rafi Baker George Christakos 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(4):427-434
Determination of uninformative prior distributions is essential in many branches of knowledge integration and system processing.
The conceptual difficulties of this determination are due to lack of uniqueness and consequential lack of objectivity associated
with the state of complete ignorance. The present work overcomes the above difficulty by considering a class of priors that
are consistent with a physical invariance principle, namely, invariance with respect to a change in the system of dimensional
units. These priors do not represent total ignorance and they do not suffer from the aforementioned conceptual difficulties.
This Dimensional Invariance Requirement (DIR) leads to a class of prior densities, which constitute a generalization of Jeffrey’s
proposal concerning priors of inherently positive variables. This generalization possesses certain important features, from
a formal as well as an interpretive viewpoint, which involve the notion of a knowledge-based natural reference point of physical
random variables (RV). Conceptual difficulties associated with uninformative priors are resolved, whereas well-established
results are derived as special cases of the DIR. Application of this requirement to a system of RV yields the familiar result
that at the prior knowledge stage these variables should be considered as independent. Prior distributions for non-dimensional
physical quantities are obtained by defining these variables in terms of dimensional quantities. A logarithmic transformation
carries the physical prior into a uniform (flat) density that is convenient in certain applications. In a companion paper
we examine the improvements gained in the maximum entropy context by means of the proposed class of physical prior densities. 相似文献