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141.
The continuing public concern with overfishing ignores the underlying problems that face fishery mangers. Attention needs to be given to (1) the transitory nature of the ocean environment, (2) the natural variation in fish stocks, (3) the role of the fishing industry and market forces in fishery management, and (4) the failure to focus on what it is we most need from the oceans, in what form we need it, and at what price. 相似文献
142.
The paper presents a numerical investigation on the behaviour of reinforced concrete bridge piers subjected to horizontal seismic input. The scope of the investigation is to quantify the phenomenon of bending-induced axial vibrations. The results of a set of analyses conducted on single-column bent systems indicate that flexural cracking produces, in fact, significant axial vibrations. This effect is particularly relevant in squat elements with low axial force where the sway of the cross-sectional neutral axis under alternate bending causes strong hammering impulses at crack closure. Quantification of the effects related to this phenomenon can be determinant for the seismic assessment of existing bridges as well as for the design of new bridges. Likewise, performance and design forces of bearings and other anti-seismic devices can be estimated with more accuracy, based on the expected level of combined vertical and horizontal acceleration response on decks. The pier overall flexural response is not significantly altered by the fluctuation in axial force associated to these impulses, although local moment–curvature behaviour is, due to axial–bending interaction. Shear resisting mechanisms should be more sensitive to these vibrations and shear failure anticipated when a reduction in the axial contribution to the section shear capacity occurs. A tentative equation for the prediction of this flexural-induced vertical acceleration component is proposed based on simplified section kinematics and elastic impact analysis. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
143.
S. Foti S. Parolai P. Bergamo G. Di Giulio M. Maraschini G. Milana M. Picozzi R. Puglia 《Bulletin of Earthquake Engineering》2011,9(6):1797-1820
This paper reports on site characterization for a set of accelerometric stations of the RAN (Italian accelerometric network)
with specific attention to the shear wave velocity profile. The latter is indeed of primary importance for the usability of
the accelerometric database. Surface wave analysis has been chosen as the primary investigation method since it offers the
possibility of reaching the required accuracy with reasonable costs. A range of different techniques, both of the active-source
and passive-source types, has been adopted to cope with the objectives of the characterization in relation to specific geological
settings. Quality assessment of experimental data has been implemented to check the consistency of the measurements also with
respect to the fundamental hypotheses of the method. Strategies to improve the reliability and robustness of the surface wave
data inversion were exploited in order to mitigate problems arising from solution non-uniqueness and influence of higher modes
in the propagation. Comparisons with independent borehole tests, available at some specific sites, confirm the reliability
of the results. Although the research program covered only a subset of the network, the obtained results show the importance
of specific experimental investigations aimed at estimating the shear wave velocity profile. Indeed the results lead to a
re-classification of several sites with respect to the preliminary classification based on surface geology. Within this context,
four selected case histories are reported in the present paper. 相似文献
144.
The role of alternating outcrops of sediments and basaltic lavas on seismic urban scenario: the study case of Catania, Italy 总被引:2,自引:1,他引:1
F. Panzera R. Rigano G. Lombardo F. Cara G. Di Giulio A. Rovelli 《Bulletin of Earthquake Engineering》2011,9(2):411-439
Experimental data and numerical modelling were used to study the effect of local geology on the seismic response of the Catania
area. The town extends on a marly clays bedrock and terraced deposits made up by coastal sands and alluvial conglomerates.
This sedimentary substratum is deeply entrenched by paleo-valleys filled by lava flows and pyroclastics. Available borehole
data and elastic parameters were used to reconstruct a geotechnical model in order to perfome 1D numerical modeling. Seismic
urban scenarios were simulated considering destructive (M
w = 7.0), strong (M
w = 6.2) and moderate (M
w = 5.7) earthquakes to assess the shaking level of the different outcropping formations. For each scenario seven real accelerograms
were selected from the European Strong Motion Database to assess the expected seismic input at the bedrock. PGA and spectral
acceleration at different periods were obtained in the urban area through the equivalent linear numerical code EERA, and contour
maps of different levels of shaking were drawn. Standard and horizontal-to-vertical spectral ratios were achieved making use
of a dataset of 172 seismic events recorded at ten sites located on the main outcropping lithotypes. Spectral ratios inferred
from earthquake data were compared with theoretical transfer functions. Both experimental and numerical results confirm the
role of the geological and morphologic setting of Catania. Amplification of seismic motion mainly occurs in three different
stratigraphic conditions: (a) sedimentary deposits mainly diffused in the south of the study area; (b) spots of soft sediments
surrounded by lava flows; (c) intensely fractured and scoriaceous basaltic lavas. 相似文献
145.
G. Di Giulio S. Marzorati F. Bergamaschi P. Bordoni F. Cara E. D��Alema C. Ladina M. Massa 《Bulletin of Earthquake Engineering》2011,9(3):783-807
The 2009 Mw 6.3 L’Aquila event caused extensive damage in the city of L’Aquila and in some small towns in its vicinity. The
most severe damage was recognized SE of L’Aquila town along the Aterno river valley. Although building vulnerability and near-source
effects are strongly responsible for the high level of destruction, site effects have been invoked to explain the damage heterogeneities
and the similarities between the 2009 macroseismic field with the intensities of historical earthquakes. The small village
of Onna is settled on quaternary alluvium and suffered during the L’Aquila event an extremely heavy damage in the masonry
structures with intensity IX–X on the Mercalli-Cancani-Sieberg (MCS) scale. The village of Monticchio, far less than 1.3 km
from Onna, is mostly situated on Mesozoic limestone and suffered a smaller level of damaging (VI MCS). In the present paper,
we analyze the aftershock recordings at seismic stations deployed in a small area of the middle-Aterno valley including Onna
and Monticchio. The aim is to investigate local amplification effects caused by the near-surface geology. Because the seismological
stations are close together, vulnerability and near-source effects are assumed to be constant. The waveform analysis shows
that the ground motion at Onna is systematically characterized by large high-frequency content. The frequency resonance is
varying from 2 to 3 Hz and it is related to alluvial sediments with a thickness of about 40 m that overlay a stiffer Pleistocene
substrate. The ground motion recordings of Onna are well reproduced by the predictive equation for the Italian territory. 相似文献
146.
Di Franco A Graziano M Franzitta G Felline S Chemello R Milazzo M 《Marine pollution bulletin》2011,62(5):926-933
Many human activities add new structures to the marine landscape. Despite the fact that human structures cause some inevitable impacts, surprisingly little information exists on the effects of marina on natural marine assemblages. The aim of this paper is to assess habitat-specific response of benthic sessile organisms of rocky shores in relation to the presence of a small marina. Sampling was carried out at three coastal habitats (midshore, lowshore and subtidal) by means of visual censuses adopting an after-control-impact (ACI) experimental design. It appears that the marina affects the structure and composition of benthic communities of both the midshore and the lowshore. Little effect was evident on shallow subtidal assemblage structure. The results of the present study clearly show habitat-specific responses of coastal benthic assemblages to the presence of infrastructure. 相似文献
147.
Air pollution has been a major transboundary problem and a matter of global concern for decades. Climate change and air pollution are closely coupled. Just as air pollution can have adverse effects on human health and ecosystems, it can also impact the earth’s climate. As we enter an era of rapid climate change, the implications for air quality need to be better understood, both for the purpose of air quality management and as one of the societal consequences of climate change. In this study, an attempt has been made to estimate the current air quality to forecast the air quality index of an urban station Kolkata (22.65°N, 88.45°E), India for the next 5 years with neural network models. The annual and seasonal variability in the air quality indicates that the winter season is mostly affected by the pollutants. Air quality index (AQI) is estimated as a geometric mean of the pollutants considered. Different neural network models are attempted to select the best model to forecast the AQI of Kolkata. The meteorological parameters and AQI of the previous day are utilized to train the models to forecast the AQI of the next day during the period from 2003 to 2012. The selection of the best model is made after validation with observation from 2013 to 2015. The radial basis functional (RBF) model is found to be the best network model for the purpose. The RBF model with various architectures is tried to obtain precise forecast with minimum error. RBF of 5:5-91-1:1 structure is found to be the best fit for forecasting the AQI of Kolkata. 相似文献
148.
149.
Giulio Morteani Y. Kostitsyn C. Preinfalk H. A. Gilg 《International Journal of Earth Sciences》2010,99(4):927-947
The amethyst-bearing geodes found in the flood basalts of the Arapey formation at Artigas (Uruguay) were formed as protogeodes
by bubbles of CO2-rich basalt-derived fluids. The formation of the celadonite rim and the lining of the geodes by agate followed by quartz
and amethyst were driven by the artesian water of the Guaraní aquifer percolating the basalts from below. The temperature
of the amethyst formation is estimated from fluid inclusion data to be between 50° and 120°C. Oxygen stable isotope data suggest
a crystallization temperature of calcite of about only 24°C. The actual wellhead temperature of the water produced from the
Guaraní aquifer in the study area is around 29°C. 相似文献
150.
Two case histories are presented to give evidences for sediment cooling during increasing burial depth due to heat flow decrease at the end of crustal stretching in extensional settings. The first refers to the Lower Cretaceous succession accumulated in a strongly subsiding trough within the Sirt Basin (Libya); the second relates to the Mesozoic succession of the Lombardian Basin (NW Italy) formed during Late Triassic–Early Jurassic rifting of the northern margin of the Adriatic microplate. In both cases, heat flow decreasing at the end of crustal stretching overbalanced the thermal effect of increasing burial depth causing a net cooling of rocks. These examples provide an alternative to exhumation for explaining cooling events recorded by rifting sedimentary sequences. 相似文献