首页 | 官方网站   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   111篇
  国内免费   1篇
  完全免费   52篇
地球科学   164篇
  2018年   1篇
  2017年   3篇
  2016年   6篇
  2015年   17篇
  2014年   17篇
  2013年   18篇
  2012年   8篇
  2011年   12篇
  2010年   5篇
  2009年   8篇
  2008年   6篇
  2007年   7篇
  2006年   7篇
  2005年   4篇
  2004年   2篇
  2003年   4篇
  2002年   2篇
  2001年   1篇
  2000年   2篇
  1998年   3篇
  1997年   1篇
  1996年   4篇
  1995年   7篇
  1994年   3篇
  1993年   4篇
  1992年   1篇
  1991年   3篇
  1990年   1篇
  1989年   1篇
  1988年   1篇
  1986年   1篇
  1981年   2篇
  1976年   1篇
  1972年   1篇
排序方式: 共有164条查询结果,搜索用时 46 毫秒
1.
Summary A shallow and short-lived subsynoptic cyclone is discussed as one of typical events causing natural disasters over Saudi Arabia on 5 January 2002 using the Japan Meteorological Agency global analysis dataset. The main cause for its formation was vorticity stretching. On the same day widespread rainfall over Saudi Arabia with enhanced precipitation over the mountainous Jeddah region was also observed using the Global Precipitation Climatology Project dataset. Owing to eastward-moving wintertime synoptic-scale Mediterranean disturbances, this rainfall was associated with frontal activity, modified by the local orography.  相似文献   
2.
3.
4.
5.
The statistics of level crossings and local extremes in concentration fluctuations in plumes dispersing in the atmosphere have been investigated. A set of concentration fluctuation tracer experiments has been utilized to measure the statistical propertics of the upcrossing interval (inter-arrival time between consecutive concentration bursts), excursion duration (persistence or width of concentration bursts), and concentration amplitude (difference between the maximum and minimum concentrations between successive upcrossings) with respect to a range of concentration crossing levels. In particular, the effect of downwind distance and atmospheric stratification on the level-crossing statistics has been studied in detail. It is shown that the effect of increasing atmospheric stability on level-crossing statistics is similar to the effect of increasing distance from the source in the sense that level-crossing statistics of concentration fluctuations in stable stratification resemble those in neutral stratification, but at a greater downwind distance. It is also found that the distribution of the interval between consecutive upcrossings of a concentration level, as well as the duration of an excursion across a concentration level, can be approximated by a lognormal distribution, whereas the distribution of the concentration amplitude is best characterized by a gamma distribution. Some implications of these results for the modeling of level-crossing statistics of concentration fluctuations are discussed.  相似文献   
6.
This paper describes a study of the vertical structure of concentration fluctuations in a neutrally buoyant plume from an elevated point source in slightly convective to moderately stable meteorological conditions at ranges of between 12.5 and 100 m for a range of source heights between 1 and 5 m. Observations were made of concentration fluctuations in a dispersing plume using a vertical array of sixteen very fast-response photoionization detectors placed at heights between 0.5 and 16 m. Vertical profiles of a number of concentration statistics were extracted, namely, mean concentration, fluctuation intensity, intermittency factor, peak-to-mean concentration ratio, mean dissipation rate of concentration variance, and various concentration time and length scales of dominant motions in the plume (e.g., integral macro-scale, in-plume mid-scale and Taylor micro-scale). The profiles revealed a similarity to corresponding crosswind profiles for a fully elevated plume, but showed greater and greater departure from the latter shapes once the plume had grown in the vertical so that its lower dege began to interact progressively more strongly with the ground. The evolution of the concentration probability density function at a fixed range, but with decreasing height from the ground, is similar to that obtained at a fixed height but with increasing distance from the source. Concentration power spectra obtained at different heights all had an extensive inertial-convective subrange spanning at least two decades in frequency, but spectra measured near the ground had a greater proportion of the total concentration variance in the lower frequencies (energetic subrange), with a correspondingly smaller proportion in the higher frequencies (inertial-convective subrange). It is believed that these effects result from the increased mean shear near the surface, and blocking by the surface. The effect of enhanced shear-induced molecular diffusion on concentration fluctuations is examined.  相似文献   
7.
8.
A meandering plume model that explicitly incorporates the effects of small-scale structure in the instantaneous plume has been formulated. The model requires the specification of two physically based input parameters; namely, the meander ratio,M, which is dependent on the ratio of the meandering plume dispersion to the instantaneous relative plume dispersion and, a relative in-plume fluctuation measure,k, that is related inversely to the fluctuation intensity in relative coordinates. Simple analytical expressions for crosswind profiles of the higher moments (including the important shape parameters such as fluctuation intensity, skewness, and kurtosis) and for the concentration pdf have been derived from the model. The model has been tested against some field data sets, indicating that it can reproduce many key aspects of the observed behavior of concentration fluctuations, particularly with respect to modeling the change in shape of the concentration pdf in the crosswind direction.List of Symbols C Mean concentration in absolute coordinates - C r Mean concentration in relative coordinates - C0 Centerline mean concentration in absolute coordinates - C r,0 Centerline mean concentration in relative coordinates - f Probability density function of concentration in absolute coordinates - f c Probability density function of plume centroid position - f r Probability density function of concentration in relative coordinates - i Absolute concentration fluctuation intensity (standard deviation to mean ratio) - i r Relative concentration fluctuation intensity (standard deviation to mean ratio) - k Relative in-plume fluctuation measure:k=1/i r 2 - K Concentration fluctuation kurtosis - M Meander ratio of meandering plume variance to relative plume variance - S Concentration fluctuation skewness - x Downwind distance from source - y Crosswind distance from mean-plume centerline - z Vertical distance above ground - Instantaneous (random) concentration - Crosswind dispersion ofnth concentration moment about zero - ny Mean-plume crosswind (absolute) dispersion - y Plume centroid (meandering) dispersion in crosswind direction - y,c Instantaneous plume crosswind (relative) dispersion - Normalized mean concentration in absolute coordinates:C/C 0 - Particular value taken on by instantaneous concentration,   相似文献   
9.
C. S. Joy 《Climatic change》1993,25(3-4):335-351
Four surveys were conducted to assess the cost of direct and indirect flood damage to the New South Wales town of Nyngan, which was inundated in the 4–6 hour period after its flood protection levees were breached on 23 April 1990. A survey of flood damage to 24 residential properties, 14 commercial properties and 6 public authority properties was made by personal inspection. Surveys of flood damage to other public properties, of the worth of the volunteer effort in the evacuation, clean-up and recovery phases of the disaster, and of the value of donated goods and money were made by telephone and letter. The results of all surveys are presented and discussed. The use of a computer model to estimate property damage throughout the flooded area is described. Finally, the total cost of flood damage in Nyngan ($47.3 million) is dissected by type of damage, property sector and community sector.  相似文献   
10.
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