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排序方式: 共有112条查询结果,搜索用时 31 毫秒
81.
Nikolaos Friligos 《Marine pollution bulletin》1982,13(3):103-106
Observations in Elefsis Bay, an anoxic basin in the Saronikos Gulf, indicate that the large accumulation of ammonia, phosphates and silicates in the deep water are the result of the decomposition of organic matter during the anoxic period. The processes of denitrification, nitrate reduction and organic decomposition are also evident. Ammonia predominates in the inorganic fraction within the whole water column. 相似文献
82.
Gerassimos Mineshos Nikolaos Roumelis Efthalia Evmorfopoulou Sotirios Glavas 《Journal of Atmospheric Chemistry》1991,13(4):343-357
The nitric acid formed from trans-2-butene, propene, ethene, toluene, and n-butane in single hydrocarbon/NO2/purified air systems was examined in smog chamber experiments. The effect of hydrocarbon and NO2 concentrations on the maximum HNO3 yield, defined as percentages of initial NO2 converted to HNO3, was studied in two sets of experiments. In every hydrocarbon system, we found no effect of hydrocarbon concentration variation on the nitric acid formed. Out of initially added 100 ppb NO2, in the hydrocarbon-rich systems, ethene formed most HNO3 (45%), followed by propene, toluene, and n-butane (24%), and trans-2-butene (13%). When the initial NO2 concentration was varied with a constant hydrocarbon concentration, the amount of HNO3 formed was found to linearly increase with the added NO2 down to |HC|/|NO2| ratios, which depended on the nature of the hydrocarbon studied. The initial rate of HNO3 formation in hydrocarbon excess experiments varied between 50, 35, 23, 16, and 8 ppb/hr for butene, propene, toluene, ethene, and butane systems, respectively. 相似文献
83.
Nikolaos Athanasiadis Spassimir Tonkov Juliana Atanassova Elissaveta Bozilova 《Journal of Paleolimnology》2000,24(3):331-342
A palynological investigation was conducted on two cores with Holocene sediments collected from the northeastern littoral part of the border Lake Doirani in northern Greece. The radiocarbon dates indicated that the analyzed sediments accumulated during the last 5000 yrs. The pollen-stratigraphic record revealed the environmental changes in the catchment area, starting from a natural undisturbed landscape to one modified by increasing anthropogenic influences. The tree vegetation dominated by Quercus woods in the lowlands and byPinus, Abies, and Fagus at higher altitudes, lasted for the period 2900 - 830 cal. B.C. Subsequently it was replaced by xerothermic herb and tree vegetation as a result of intensive human activity - and farming and stock-breeding. The accumulation of sediments with more sand and gravel in historical time was the result of increased erosion. 相似文献
84.
Nikolaos Efthimiou 《水文科学杂志》2019,64(9):1095-1116
The study aims to investigate the effect of soil properties delineation on erosion modelling. To that end, the soil attributes of the Venetikos River catchment, northwestern Greece, are described using two pedological datasets, i.e. field samples and classification maps. The goal is to select the most appropriate for the accurate estimation of erosion. The Revised Morgan-Morgan-Finney (RMMF) model is developed per base map (annual or multi-annual), keeping all other parameters unchanged. Modelled sediment yield (SY) values are validated against “observed” ones, calculated utilizing the sediment rating curve methodology. Overall, the classification maps approach (164.35 t km-2 year?1) performed better than the soil samples one (82.97 t km-2 year?1), displaying higher convergence to the synthetic SY (548.9 t km-2 year?1). The discrepancy among approaches is attributed to the different computation methodologies (thus pedological background) used. Both approximations successfully identified the high-risk erosion areas. The same conclusions arose from the multi-annual application of the model. 相似文献
85.
The relationship between altitude of meteorological stations and average monthly and annual precipitation 总被引:2,自引:0,他引:2
Markos Gouvas Nikolaos Sakellariou Fotios Xystrakis 《Studia Geophysica et Geodaetica》2009,53(4):557-570
The aim of this study was to prove that altitudinal variability of average monthly and annual precipitation is better summarised
when the altitude observed within a radius of several kilometres around a meteorological station is taken into consideration,
instead of the altitude of the station itself. The use of the variable Z′, which combines the altitude of the closest mountain
with its distance from the station, is compared against the use of altitude alone in simple linear and multiple quadratic
regression equations for the altitudinal interpolation of precipitation over Greece. The data-set comprised precipitation
observations from 516 meteorological stations. The comparison between the two variables is discussed on the basis of the resulting
determination coefficients (R2) and standard errors of estimate (S). For all seasons, except summer, it was found that the variable Z′ improves the predictive
ability of the regression equations, thus showing its potential for further use in interpolation procedures. 相似文献
86.
Nikolaos Andronikidis Eleni Kokinou Antonios Vafidis Evangelos Kamberis Emmanouil Manoutsoglou 《Marine Geophysical Researches》2018,39(4):475-490
Seismic reflection data and bathymetry analyses, together with geological information, are combined in the present work to identify seabed structural deformation and crustal structure in the Western Mediterranean Ridge (the backstop and the South Matapan Trench). As a first step, we apply bathymetric data and state of art methods of pattern recognition to automatically detect seabed lineaments, which are possibly related to the presence of tectonic structures (faults). The resulting pattern is tied to seismic reflection data, further assisting in the construction of a stratigraphic and structural model for this part of the Mediterranean Ridge. Structural elements and stratigraphic units in the final model are estimated based on: (a) the detected lineaments on the seabed, (b) the distribution of the interval velocities and the presence of velocity inversions, (c) the continuity and the amplitudes of the seismic reflections, the seismic structure of the units and (d) well and stratigraphic data as well as the main tectonic structures from the nearest onshore areas. Seabed morphology in the study area is probably related with the past and recent tectonics movements that result from African and European plates’ convergence. Backthrusts and reverse faults, flower structures and deep normal faults are among the most important extensional/compressional structures interpreted in the study area. 相似文献
87.
Optimal multi-step collocation: application to the space-wise approach for GOCE data analysis 总被引:5,自引:3,他引:2
Collocation is widely used in physical geodesy. Its application requires to solve systems with a dimension equal to the number
of observations, causing numerical problems when many observations are available. To overcome this drawback, tailored step-wise
techniques are usually applied. An example of these step-wise techniques is the space-wise approach to the GOCE mission data
processing. The original idea of this approach was to implement a two-step procedure, which consists of first predicting gridded
values at satellite altitude by collocation and then deriving the geo-potential spherical harmonic coefficients by numerical
integration. The idea was generalized to a multi-step iterative procedure by introducing a time-wise Wiener filter to reduce
the highly correlated observation noise. Recent studies have shown how to optimize the original two-step procedure, while
the theoretical optimization of the full multi-step procedure is investigated in this work. An iterative operator is derived
so that the final estimated spherical harmonic coefficients are optimal with respect to the Wiener–Kolmogorov principle, as
if they were estimated by a direct collocation. The logical scheme used to derive this optimal operator can be applied not
only in the case of the space-wise approach but, in general, for any case of step-wise collocation. Several numerical tests
based on simulated realistic GOCE data are performed. The results show that adding a pre-processing time-wise filter to the
two-step procedure of data gridding and spherical harmonic analysis is useful, in the sense that the accuracy of the estimated
geo-potential coefficients is improved. This happens because, in its practical implementation, the gridding is made by collocation
over local patches of data, while the observation noise has a time-correlation so long that it cannot be treated inside the
patch size. Therefore, the multi-step operator, which is in theory equivalent to the two-step operator and to the direct collocation,
is in practice superior thanks to the time-wise filter that reduces the noise correlation before the gridding. The criteria
for the choice of this filter are investigated numerically. 相似文献
88.
89.
The contribution of anthropogenic forcings to regional changes in temperature during the last decade
Nikolaos Christidis Peter A. Stott Francis W. Zwiers Hideo Shiogama Toru Nozawa 《Climate Dynamics》2012,39(6):1259-1274
Regional distributions of the mean annual temperature in the 2000s are computed with and without the effect of anthropogenic influences on the climate in several sub-continental regions. Simulated global patterns of the temperature response to external forcings are regressed against observations using optimal fingerprinting. The global analysis provides constraints which are then used to construct the regional temperature distributions. A similar approach was also employed in previous work, but here the methodology is extended to examine changes in any region, including areas with a poor observational coverage that were omitted in the earlier study. Two different General Circulation Models (GCMs) are used in the analysis. Anthropogenic forcings are found to have at least quadrupled the likelihood of occurrence of a year warmer than the warmest year since 1900 in 23 out of the 24 regions. The temperature distributions computed with the two models are very similar. While a more detailed assessment of model dependencies remains to be made once additional suitable GCM simulations become available, the present study introduces the statistical methodology and demonstrates its first application. The derived information concerning the effect of human influences on the regional climate is useful for adaptation planning. Moreover, by pre-computing the change in the likelihood of exceeding a temperature threshold over a range of thresholds, this kind of analysis enables a near real-time assessment of the anthropogenic impact on the observed regional temperatures. 相似文献
90.
Nikolaos Georgakarakos 《Monthly notices of the Royal Astronomical Society》2009,392(3):1253-1263
In a series of papers, we developed a technique for estimating the inner eccentricity in hierarchical triple systems, with the inner orbit being initially circular. However, for certain combinations of the masses and the orbital elements, the secular part of the solution failed. In this paper, we derive a new solution for the secular part of the inner eccentricity, which corrects the previous weakness. The derivation applies to hierarchical triple systems with coplanar and initially circular orbits. The new formula is tested numerically by integrating the full equations of motion for systems with mass ratios from 10−3 to 103 . We also present more numerical results for short-term eccentricity evolution, in order to get a better picture of the behaviour of the inner eccentricity. 相似文献