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   5篇
  免费   0篇
地球物理   1篇
地质学   2篇
海洋学   2篇
  2018年   2篇
  2012年   1篇
  2009年   1篇
  2007年   1篇
排序方式: 共有5条查询结果,搜索用时 15 毫秒
1
1.
Different aspects of reproductive biology of the polychaete Timarete filigera (Delle Chiaje) were studied during a period of 2 years (from September 2002 to August 2003 and from September 2004 to August 2005). Timarete filigera specimens were collected monthly in the port of Bari (South Adriatic Sea, Mediterranean Sea). For population analysis, regenerating and entire specimens were separately analyzed, the regenerating individuals were assigned to different categories related to the region of the body from which they derived. Regenerating individuals were present throughout the year. There were three to four times more individuals deriving from the middle part than the anterior and posterior regenerating portions. From the high percentage of regenerating individuals observed in the T. filigera population, it can be supposed that this species reproduces mainly asexually by schizogenesis. However, histological analysis revealed the presence of female gametes in a few individuals. In contrast, males were never collected, probably due to the limited number of reproductive individuals collected. The abundance has shown wide fluctuations during the year, with a decrease from Winter to Spring. The analysis of the size‐frequency histograms has shown a growing phase of whole specimens from Spring to Winter. The life cycle of the investigated species is discussed with the hypothesis that strategies could be linked to the colonized environments, agamic reproduction coupled with sexual reproduction assures the presence and expansion of the population after the colonization by a limited number of larvae.  相似文献   
2.
Measurements of particle size-fractionated POC/234Th ratios and 234Th and POC fluxes were conducted using surface-tethered, free-floating, sediment traps and large-volume in-situ pumps during four cruises in 2004 and 2005 to the oligotrophic eastern Mediterranean Sea and the seasonally productive western Mediterranean and northwest Atlantic. Analysis of POC/234Th ratios in sediment trap material and 10, 20, 53, 70, and 100 μm size-fractionated particles indicate, for most stations, decreasing ratios with depth, a weak dependence on particle size, and ratios that converge to ~1–5 μmol dpm?1 below the euphotic zone (~100–150 m) throughout the contrasting biogeochemical regimes. In the oligotrophic waters of the Aegean Sea, 234Th and POC fluxes estimated using sediment traps were consistently higher than respective fluxes estimated from water-column 234Th–238U disequilibrium, observations that are attributed to terrigenous particle scavenging of 234Th. In the more productive western Mediterranean and northwest Atlantic, 234Th and POC fluxes measured by sediment trap and 234Th–238U disequilibrium agreed within a factor of 2–4 throughout the water column. An implication of these results is that estimates of POC export by sediment traps and 234Th–238U disequilibrium can be biased differently because of differential settling speeds of POC and 234Th-carrying particles.  相似文献   
3.
International Journal of Earth Sciences - The P-wave velocities (Vp) within the East European Craton in Poland are well known through several seismic experiments which permitted to build a...  相似文献   
4.
Seasonal changes of the primary and secondary microseisms were analysed in the wavefield of the ambient noise recorded during the entire 2014 at the “13 BB star” array located in northern Poland, composed of thirteen, symmetrically arranged, broadband seismic stations. To that, spectral analysis, seismic interferometry, surface scalar wind speed distribution, and beamforming were used. Spectral analysis allowed to observe that a splitting of the secondary microseism peak was present in winter and autumn, and that the primary microseism peak was visible in spring, summer and autumn. Using seismic interferometry, the long-term characteristics of the noise wavefield were recognized. The seasonal variations of the secondary microseism source were described by means of the analysis of the surface scalar wind speed for each month. The splitting of the secondary peak was attributed to the interaction of a strong wind blowing from the North Sea with a weak wind blowing from the Baltic Sea. The seasonal variations of the primary microseism peak were characterized through the frequency-domain beamforming. The peak was identified during spring, summer and autumn, when the generated wavefield was coming from the Baltic Sea. The velocity of the wavefield was evaluated within the 2.0–5.0 km/s range. The described mechanism of generation of the microseisms, based on the interaction of the nearby winds, was found to be consistent with the models reported in the literature.  相似文献   
5.
Rainfall-induced landslide susceptibility zonation of Puerto Rico   总被引:9,自引:4,他引:5  
Landslides are a major geologic hazard with estimated tens of deaths and $1–2 billion in economic losses per year in the US alone. The island of Puerto Rico experiences one or two large events per year, often triggered in steeply sloped areas by prolonged and heavy rainfall. Identifying areas susceptible to landslides thus has great potential value for Puerto Rico and would allow better management of its territory. Landslide susceptibility zonation (LSZ) procedures identify areas prone to failure based on the characteristics of past events. LSZs are here developed based on two widely applied methodologies: bivariate frequency ratio (FR method) and logistic regression (LR method). With these methodologies, the correlations among eight possible landslide-inducing factors over the island have been investigated in detail. Both methodologies indicate aspect, slope, elevation, geological discontinuities, and geology as highly significant landslide-inducing factors, together with land-cover for the FR method and distance from road for the LR method. The LR method is grounded in rigorous statistical testing and model building but did not improve results over the simpler FR method. Accordingly, the FR method has been selected to generate a landslide susceptibility map for Puerto Rico. The landslide susceptibility predictions were tested against previous landslide analyses and other landslide inventories. This independent evaluation demonstrated that the two methods are consistent with landslide susceptibility zonation from those earlier studies and showed this analysis to have resulted in a robust and verifiable landslide susceptibility zonation map for the whole island of Puerto Rico.  相似文献   
1
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