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31.
32.
Andreas J. Kappos Georgios Panagopoulos Christos Panagiotopoulos Gregorios Penelis 《Bulletin of Earthquake Engineering》2006,4(4):391-413
The methodology followed by the Aristotle University (AUTh) team for the vulnerability assessment of reinforced concrete (R/C) and unreinforced masonry (URM) structures is presented. The paper focuses on the derivation of vulnerability (fragility) curves in terms of peak ground acceleration (PGA), as well as spectral displacement (s
d), and also includes the estimation of capacity curves, for several R/C and URM building types. The vulnerability assessment methodology is based on the hybrid approach developed at AUTh, which combines statistical data with appropriately processed (utilising repair cost models) results from nonlinear dynamic or static analyses, that permit extrapolation of statistical data to PGA’s and/or spectral displacements for which no data are available. The statistical data used herein are from earthquake-damaged greek buildings. An extensive numerical study is carried out, wherein a large number of building types (representing most of the common typologies in S. Europe) are modelled and analysed. Vulnerability curves for several damage states are then derived using the aforementioned hybrid approach. These curves are subsequently used in combination with the mean spectrum of the Microzonation study of Thessaloniki as the basis for the derivation of new vulnerability curves involving spectral quantities. Pushover curves are derived for all building types, then reduced to standard capacity curves, and can easily be used together with the S
d fragility curves as an alternative for developing seismic risk scenarios. 相似文献
33.
Zafeiria Roumelioti Anastasia Kiratzi Nikos Theodoulidis Christos Papaioannou 《Journal of Seismology》2002,6(2):219-236
S-wave spectral analysis is applied to 174 strong motion accelerationrecords to obtain the source parameters of 27 aftershocks(3.1 ML 4.3) of the May 13, 1995, Mw 6.6,Kozani-Grevena (NW Greece) earthquake. The data are derived from atemporary network, of three-component digital accelerographs, deployedwithin the strongly affected area some days after the mainshock occurrence.Site effects were evident in the strong motion records at 3 out of the 4stations used, and a correction was applied to account for theoverestimation of seismic moment due to amplification of thelow-frequency part of the spectrum. The data from this analysis arecomplimented with previously obtained source parameters for earthquakesin Greece, in order to study the applicability of the empirical scalingrelations used so far, towards smaller magnitudes. In general, a goodcorrelation was observed in most cases, validating the use of empiricalrelations that are applicable to the Aegean area. Empirical relations aredetermined between seismic moment and seismic slip, as well as, betweenseismic moment and stress drop, applicable to small magnitude earthquakes(ML < 4.3). Stress drop values were found to be relatively small,ranging from 2 to 41 bars, indicative of inter-plate environments. Thevalues of fc and of fmax were found in good agreement withrelations based on observations from larger worldwide earthquakes. 相似文献
34.
Christos Pennos Stein-Erik Lauritzen Konstantinos Vouvalidis Patience Cowie Sofia Pechlivanidou Charikleia Gkarlaouni Michael Styllas Panagiotis Tsourlos Antonios Mouratidis 《地球表面变化过程与地形》2019,44(9):1710-1721
We present an integrated study of subsurface and surficial karst landforms to unravel the uplift history of karst landscape in a tectonically-active area. To this end, we apply a multidisciplinary approach by combining cave geomorphology and Th/U dating of speleothems with remote sensing plus geophysical imaging of surface landforms. We use as an example Mt. Menikio in northern Greece where four caves share well-defined epiphreatic/shallow phreatic characteristics that are related to the distribution of surface and buried doline fields and provide evidence for three distinct water table stillstands (e.g. expressed as cave levels) now lying at ~130 m, ~800 m and ~1600 m a.m.s.l. Our dating constraints delimit the age of the lower water table stillstand prior to 77 ka ago and imply a maximum rate of relative base level drop of 0.45 mma-1, which is consistent with relative tectonic uplift rate estimates along currently active normal faults. We interpret the elevation of the higher water table stillstands to reflect earlier phases of uplift related to the regional tectonic events associated with the development of the North Anatolian Fault and the Northern Aegean area. Our analysis shows that the combined study of epiphreatic/shallow phreatic caves and surficial karst landforms together, is a robust way to investigate the uplift history of a karst landscape in a tectonically-active setting. © 2019 John Wiley & Sons, Ltd. 相似文献
35.
Simulating maximum and minimum temperature over Greece: a comparison of three downscaling techniques 总被引:1,自引:0,他引:1
E. Kostopoulou C. Giannakopoulos C. Anagnostopoulou K. Tolika P. Maheras M. Vafiadis D. Founda 《Theoretical and Applied Climatology》2007,90(1-2):65-82
Summary Statistical downscaling techniques have been developed for the generation of maximum and minimum temperatures in Greece. This
research focuses on the four conventional seasons, and three downscaling approaches, Multiple Linear Regression using a circulation
type approach (MLRct), Canonical Correlation Analysis (CCA) and Artificial Neural Networks (ANNs), are employed and compared
to assess their performance skills. Models were developed individually for each variable (Tmax, Tmin), station and season. The accuracy of downscaled values has been quantified in terms of a number of performance criteria,
such as differences of the mean and standard deviation ratios between observed and modelled data, the correlation coefficients
of the two sets, and also the RMSEs of the downscaled values relative to the observed. All methods revealed that during the
cool season Tmax tends to be better reproduced, whereas Tmin is overestimated, particularly over western Greece, which is characterised by higher orography. With respect to the warm
season, the simulation of Tmax reveals greater divergence, whereas Tmin is better generated. The distinction between the three techniques is somewhat blurred. None of the methods were found to
be superior to the others and each has been shown to be a good estimator in some cases. This study concludes that all proposed
methods comprise useful tools for simulating daily temperatures, as the high correlation coefficients, between observed and
downscaled values, have demonstrated. However, the importance of local factors, which affect the natural variability of temperature,
has been emphasised indicating that the geography of a region constitutes an important and rather complex factor, which should
be included in models to improve their performance. 相似文献
36.
37.
A list of nearly 350 flares accompanied by type IV radio bursts by Krüger et al. (1971), which covers a period of 14 yr (1956–1969), was expanded to include all PCA and solar cosmic ray events during this entire period. This list, which includes practically all of the most energetic events during the maxima of two consecutive solar cycles, was used to investigate the latitudinal distribution of the above-mentioned flares, as well as of all PCA events, solar cosmic ray events and plage regions associated with them.Histograms of these occurences show clearly the appearance of two peaks in both solar maxima, which confirm the observations of Gnevyshev (1967). Latitudinal analysis of these histograms shows that in cycle 20 the two peaks are independent and their relative strength varies strongly with latitude. In cycle 19, however, this effect is not clearly evident, possibly because of the extremely high level of activity during this cycle. In both cycles, the second maximum shows the highest concentration of the most energetic events.During 1971–1972 visiting Professor of Astrophysics at the National University of Athens, Athens, Greece. 相似文献
38.
Circulation changes in the free atmosphere during proton events associated with type IV radio bursts
Christos S. Zerefos 《Planetary and Space Science》1975,23(7):1035-1043
New evidence of statistically significant circulation changes in the lower stratosphere and in the middle and upper troposphere following Type IV Proton and Ground Level Events confirms some earlier findings of a relationship between solar activity and weather. The maximum 24-hr circulation changes appear to occur in the North Pacific-Alaskan area. A comparison between the effects that followed the flare sample used in this study with earlier results reported for less intense solar particle emission flare samples, implies that if these particles are responsible for triggering the atmospheric circulation in times of enhanced solar activity, their atmospheric effect is enhanced as we move to the more energetic solar proton events. The physical explanation of the results may possibly be found in numerical-experimental models. Some possible causes of the results are discussed. 相似文献
39.
40.
Kostas Kalabokidis Nikolaos Athanasis Christos Vasilakos Palaiologos Palaiologou 《International journal of geographical information science》2014,28(3):541-552
Effective wildfire management is an essential part of forest firefighting strategies to minimize damage to land resources and loss of human lives. Wildfire management tools often require a large number of computing resources at a specific time. Such computing resources are not affordable to local fire agencies because of the extreme upfront costs on hardware and software. The emerging cloud computing technology can be a cost- and result-effective alternative. The purpose of this paper is to present the development and the implementation of a state-of-the-art application running in cloud computing, composed of a wildfire risk and a wildfire spread simulation service. The two above applications are delivered within a web-based interactive platform to the fire management agencies as Software as a Service (SaaS). The wildfire risk service calculates and provides daily to the end-user maps of the hourly forecasted fire risk for the next 112 hours in high spatiotemporal resolution, based on forecasted meteorological data. In addition, actual fire risk is calculated hourly, based on meteorological conditions provided by remote automatic weather stations. Regarding the wildfire behavior simulation service, end users can simulate the fire spread by simply providing the ignition point and the projected duration of the fire, based on the HFire algorithm. The efficiency of the proposed solution is based on the flexibility to scale up or down the number of computing nodes needed for the requested processing. In this context, end users will be charged only for their consumed processing time and only during the actual wildfire confrontation period. The system utilizes both commercial and open source cloud resources. The current prototype is applied in the study area of Lesvos Island, Greece, but its flexibility enables expansion in different geographical areas. 相似文献