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   59篇
  免费   3篇
测绘学   3篇
大气科学   6篇
地球物理   14篇
地质学   22篇
海洋学   14篇
天文学   1篇
自然地理   2篇
  2021年   1篇
  2020年   2篇
  2019年   1篇
  2018年   3篇
  2017年   3篇
  2016年   4篇
  2015年   2篇
  2014年   1篇
  2013年   4篇
  2012年   3篇
  2011年   6篇
  2010年   2篇
  2009年   6篇
  2008年   6篇
  2007年   3篇
  2006年   1篇
  2003年   3篇
  2002年   2篇
  2001年   3篇
  2000年   1篇
  1999年   1篇
  1998年   1篇
  1993年   1篇
  1991年   1篇
  1957年   1篇
排序方式: 共有62条查询结果,搜索用时 265 毫秒
21.
Abstract

Joint probabilities of runup height due to astronomical tides and tsunamis are calculated for five bays on the Pacific Ocean coast of Mexico. Runup heights equaled or exceeded on the average of once per 100 years, and once per 200 years, for those bays, are evaluated. Calculations are based on wave height probabilities obtained from sets of harmonic constituents and tsunami heights recorded during the last 28 years at tidal stations on each location.

Extension of potential tsunami terrestrial flooding for populated coastal zones around those bays can be determined from the previous results. One case is illustrated showing endangered features in the hazardous zones, and recommendations to prevent casualties and property damages are given.  相似文献   
22.
The earliest known record of an aurora sighting in North America was made by Jesuit missionaries in New Brunswick, Canada, in the year 1611. Here, we wish to report an earlier record made in 1602 by the Notary Public of the Spanish Manila Galleon “San Antonio de Padua” while sailing near the coast of California. We also include a brief account of the circumstances and peculiar concurrence of events leading to the 1602 sighting.  相似文献   
23.
Mineral particles could have influenced on the climate of Oviedo, a non-industrial city situated in the centre of an industrial zone of the North of Spain, increasing the temperature and the precipitations, in spite of the fact that “greenhouse gases” concentrations have diminished in this city in recent years. The directive (1999/30/EC) of the European Commission began to be applied in Oviedo in the year 2003. In agreement with this norm, our first aim was the identification of the inorganic particulate matter of the PM10 and PM2.5 fractions sampled in this city. X-ray diffraction and scanning electron microscopy coupled with X-ray dispersive energy spectrometry were used. The percentages of the different mineral phases of the PM were obtained by a Rietveld refinement of powder X-ray diffraction data. The compositions of the PM10 and PM2.5 fractions of this city are similar. Sulphates are the most abundant particles in the both fractions. Most sulphates, nitrates and sal-ammoniac would have formed by reaction between solid, liquid and/or gas particles and they could be associated with the power stations near to the city and traffic. Wüstite and haematites come from the iron and steel industries of Gijón and Avilés. The main natural sources of halite and carbonates and silicates are sea spray and soil resuspension by the wind, respectively.  相似文献   
24.
Currently, monitoring tools can be deployed in observation boreholes to better assess groundwater flow, flux of dissolved contaminants and their mass discharge in an aquifer. The relationship between horizontal water velocity in observation boreholes and Darcy fluxes in the surrounding aquifer has been studied for natural flow conditions (i.e., no pumping). Interpretation of measurements taken with dilution tests, the colloidal borescope, the Heat Pulse Flowmeter, and other techniques require the conversion of observed borehole velocity u to aquifer Darcy flux q . This conversion is typically done through a proportionality factor α = u/q . In experimental studies as well as in theoretical developments, reported values of α vary almost three orders of magnitude (from 0.5 to 10). This large variability in reported values of α could be explained by: (1) unclear distinction between Darcy flux and water seepage velocity, (2) unclear definition of water velocity in the borehole, (3) effects of well screen and the presence of the measurement device itself on the observable velocities, and (4) hydraulic conditions in the borehole annulus. We address (1), (2) from a conceptual/theoretical perspective, and (3) by means of numerical simulations. We show that issue (1) in low porosity aquifers can yield to order-of-magnitude discrepancies in estimates of q ; (2) may result in discrepancies of up to 50%, and (3) can cause differences up to 20% of water velocity in the borehole void space compared to the theoretical case of an open borehole.  相似文献   
25.
This paper discusses the effects of water quality on the hydrological and erosion response of non‐saline, non‐sodic soils during simulated rain experiments. It is well known that rain water quality affects the behaviour of saline soils. In particular, rain simulation experiments cannot be run using tap water if realistic values of infiltration rates and soil erosion are to be found. This paper reports on similar effects for non‐saline, non‐sodic soils. Two soils – a well‐aggregated clay‐rich soil developed on marine silty clay deposits and a soil developed on silt loam – were selected and subjected to a series of simulated rainstorms using demineralized water and tap water. The experiments were conducted in two different laboratories in order to obtain results independent of the tap water quality or the rainfall simulator characteristics. The results indicate that time‐to‐ponding is largely delayed by solute‐rich water (tap water). When tap water is used, infiltration rates are significantly overestimated, i.e. by more than 100 per cent. Interrill erosion rates increase by a factor of 2·5–3 when demineralized water is used. The silty clay soil was more affected by the water quality than the silt loam soil, with respect to infiltration and runoff production. Regarding interrill erosion rates, the two tested soils were similarly affected by the water quality. Therefore, it can be concluded that rainfall simulation experiments with non‐dispersive soils (e.g. non‐saline, non‐sodic) must also be conducted using water with very low electrical conductivity (i.e. less than 30–50 µS cm−1), close to that of distilled water. The use of tap water certainly hampers comparisons and the relative ranking of the hydrological and erosion response of different soils, while parameter values, such as final infiltration rate or time‐to‐ponding, cannot be extrapolated and extended to natural situations. Therefore, the majority of hydrological and erosion models and parameter values measured during rainfall simulations in the past should be used with caution for all types of soils. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   
26.
The Peruvian anchovy or anchoveta (Engraulis ringens) supports the highest worldwide fishery landings and varies in space and time over many scales. Here we present the first comprehensive sub-mesocale study of anchoveta distribution in relation to the environment. During November 2004, we conducted a behavioural ecology survey off central Peru and used a series of observational and sampling tools including SST and CO2 sensors, Niskin bottles, CTD probes, zooplankton sampling, stomach content analysis, echo-sounder, multibeam sonar, and bird observations. The sub-mesoscale survey areas were chosen from mesoscale acoustic surveys. A routine coast-wide (2000 km) acoustic survey performed just after the sub-mesoscale surveys, provided information at an even larger population scale. The availability of nearly concurrent sub-mesoscale, mesoscale and coast-wide information on anchoveta distribution allowed for a unique multi-scale synthesis. At the sub-mesoscale (100s m to km) physical processes (internal waves and frontogenesis) concentrated plankton into patches and determined anchoveta spatial distribution. At the mesoscale (10s km) location relative to the zone of active upwelling (and age of the upwelled water) and the depth of the oxycline had strong impacts on the anchoveta. Finally, over 100s km the size of the productive area, as defined by the upwelled cold coastal waters, was the determining factor. We propose a conceptual view of the relative importance of social behaviour and environmental (biotic and abiotic) processes on the spatial distribution of anchoveta. Our ecological space has two y-axis; one based on self-organization (social behaviour), and the other based on the environmental processes. At scales from the individual (10s cm), to the nucleus (m), social behaviour (e.g. the need to school) drives spatial organization. At scales larger than the school, environmental forces are the main driver of fish distribution. The conceptual ecosystem models presented in this paper may provide the final links needed to develop accurate forecasts of the spatial distribution of anchoveta over multiple scales.  相似文献   
27.
28.
Total trace metals (Cd, Co, Cu, Fe, Mn, Ni, Pb, Zn), Al, and pyrite- and reactive-associated metals were measured for the first time in a microbial mat and its underlying anoxic-sulfidic sediment collected in the saltern of Guerrero Negro (GN), Baja California Sur, Mexico. It is postulated that the formation of acid volatile sulfide (AVS) and pyrite in the area of GN could be limited by the availability of reactive Fe, as suggested by its limited abundance (mat and sediment combined average value of only 19 ± 10 ??mol g?1; n = 22) as well as the low pyrite (0.89?C7.9 ??mol g?1) and AVS (0.19?C21 ??mol g?1) concentrations (for anoxic-sulfidic sediments), intermediate degrees of pyritization (12?C50%), high degrees of sulfidization (14?C100%), generally low degrees of trace metal pyritization, and slight impoverishment in total Fe. This is a surprising result considering the large potential reservoir of available Fe in the surrounding desert. Our findings suggest that pyrite formation in the cycling of trace metals in the saltern of GN is not very important and that other sedimentary phases (e.g., organic matter, carbonates) may be more important reservoirs of trace elements. Enrichment factors [EFMe = (Me/Al)sample/(Me/Al)background] of Co, Pb, and Cd were high in the mat (EFMe = 2.2 ± 0.4, 2.8 ± 1.6 and 34.5 ± 9.8, respectively) and even higher in the underlying sediment (EFMe = 4.7 ± 1.5, 14.5 ± 6.2 and 89 ± 27, respectively), but Fe was slightly impoverished (average EFFe of 0.49 ± 0.13 and 0.50 ± 0.27 in both mat and sediment). Organic carbon to pyrite-sulfur (C/S) molar ratios measured in the mat (2.9 × 102?C27 × 102) and sediment (0.81 × 102?C6.6 × 102) were, on average, approximately 77 times higher than those typically found in marine sediments (7.5 ± 2.1). These results may indicate that ancient evaporation basins or hypersaline sedimentary environments could be identified on the basis of extremely high C/S ratios (e.g., >100) and low reactive Fe.  相似文献   
29.
Theoretical and Applied Climatology - During the 1980s, a new agricultural frontier arouse in Brazil, which occupied part of the states of Maranhão, Tocantins, Piauí, and Bahia....  相似文献   
30.
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