首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   173篇
  免费   9篇
  国内免费   2篇
大气科学   15篇
地球物理   44篇
地质学   75篇
海洋学   27篇
天文学   14篇
自然地理   9篇
  2024年   1篇
  2021年   2篇
  2020年   6篇
  2019年   1篇
  2018年   4篇
  2017年   8篇
  2016年   4篇
  2015年   3篇
  2014年   9篇
  2013年   6篇
  2012年   6篇
  2011年   17篇
  2010年   7篇
  2009年   12篇
  2008年   8篇
  2007年   8篇
  2006年   4篇
  2005年   11篇
  2004年   8篇
  2003年   4篇
  2002年   7篇
  2001年   6篇
  2000年   2篇
  1999年   3篇
  1998年   3篇
  1997年   2篇
  1996年   2篇
  1995年   2篇
  1994年   3篇
  1993年   2篇
  1992年   2篇
  1990年   2篇
  1989年   2篇
  1988年   3篇
  1986年   2篇
  1984年   1篇
  1982年   3篇
  1980年   1篇
  1979年   1篇
  1976年   1篇
  1971年   1篇
  1970年   2篇
  1941年   2篇
排序方式: 共有184条查询结果,搜索用时 93 毫秒
141.
This work analyses the state of water resources in six Mediterranean islands: Corsica, Crete, Cyprus, Mallorca, Malta and Sicily. The analysis is focused on the prevailing social, economic and hydroclimatological characteristics of these islands in order to identify the main common features affecting water availability, demand and use. A detailed analysis of the state of water resources in all the considered islands has been carried out. A background of current conditions relating to freshwater availability, quality and use has been established. Different strategies to face water scarcity and enhance water quality in theislands have been assessed in a context of climate change which is a common threat. The identification of similar problems for all the islands highlights the importance of strengthening inter-islands co-operation in the field of sustainable water resources management.  相似文献   
142.
F. Viola  D. Pumo  L. V. Noto 《水文研究》2014,28(9):3361-3372
  相似文献   
143.
Mathematical Geosciences - Frequency-domain electromagnetic instruments allow the collection of data in different configurations, that is, varying the intercoil spacing, the frequency, and the...  相似文献   
144.
Two old drift units called Poti‐Malal and Seguro have been differentiated in the Río Grande basin based on relative‐age criteria, stratigraphical relationships, morphology and fission‐track dating. A tephra dated at 0.226 ± 0.025 Ma was deposited on the Poti‐Malal drift and underlies the Seguro outwash, which is inferred to equate with marine oxygen isotope stage 6. The stratigraphical position and age suggest that the tephra post‐dates the Poti‐Malal glaciation and that it is older than the Seguro drift. The Poti‐Malal glaciation must be at least as old as Early–Middle Pleistocene, and the Seguro glaciation is assigned to the penultimate glaciation. The tephra unit may have been deposited during marine oxygen isotope stage 7. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   
145.
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   
146.
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   
147.
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   
148.
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   
149.
150.
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   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号