STUDY ON MIXIS POTENTIAL OF ROTIFER RESTING EGGS（ BRACHIONUS PLICATILIS ） WITH DIFFERENT COLLECTION TIMES AND DIFFERENT PRESERVATION PERIODS   总被引：1，自引：0，他引：1  

周利郑严  相建海 《中国海洋湖沼学报》2001,19(3):222-227

The present study investigated the possible changes in the mixis potential of rotifer resting eggs produced by a single stock of Brachionus plicatilis and collected and preserved annually from 1985 - 1998. Several clones derived from each batch of resting eggs were cultured under the same conditions for 21 days. The percentage of clones appearing resting eggs and the average yield of resting eggs produced from each clone were recorded and statistically analyzed to find the differences between the mixis potential of those resting egg batches. Results showed that different batches of resting eggs had different mictic levels among their descendent clones; but no regular relationship was found between the mixis potential of resting eggs and their collection times/preservation periods. Several internal and external factors that might affect the mixis potential of resting eggs were discussed.  相似文献   

中国林业遥感发展历程   总被引：1，自引：1，他引：0  

李增元  陈尔学 《遥感学报》2021,25(1):292-301

根据林业遥感科研项目成果和行业应用表现出的阶段性特点,将中国林业遥感发展历程划分为3个阶段： 1951年—1980年为以航空遥感像片为主的目视解译应用阶段,建立了航空摄影和地面综合调查相结合的森林调查技术体系;1981年—2000年为卫星遥感开拓创新阶段,首次研发了针对森林资源调查的卫星遥感数字图像处理系统,在可再生资源遥感调查、遥感系列制图、生态效益评价等关键技术领域均取得了重大突破,并将应用领域扩展到湿地资源、荒漠化和沙化土地、林业灾害等遥感调查、监测领域;2001年—2020年为定量遥感发展与综合应用服务平台形成阶段,通过深入开展林业遥感应用基础理论和定量遥感技术与方法研究,促进了定量遥感技术的快速发展和林业综合监测技术体系的形成,并构建了林业遥感综合应用服务平台;最后就林草部门在新时期所面对的新要求、新任务,给出了未来林草遥感科研和应用发展建议。  相似文献   

Effect of rainfall and antecedent dry periods on heavy metal loading of sediments on urban roads     

Peng Tian  Yingxia Li  Zhifeng Yang 《Frontiers of Earth Science》2009,3(3):297-302

Concentration and mass loadings of heavy metals adsorbed on sediment from an urban road surface in Beijing were investigated. The buildup and washoff processes are discussed. Results showed that masses of sediments smaller than 500 μm in diameter varied from 11.2 to 25.5 g/m². On average, sediments smaller than 125 μm accounted for 42.9% of sediments smaller than 500 μm in mass. Cd, Cr, Cu, and Ni were more likely to attach to smaller sediments than bigger ones, compared to Pb and Zn. Mass loading of the sediments generally increased with antecedent dry periods, but the linear relationship was better for smaller sediments than for bigger ones. Heavy metal concentrations adsorbed on sediments with diameter less than 40 μm generally decreased more obviously than those adsorbed on bigger ones after rainfall events.  相似文献   

鸡西盆地下白垩统城子河—穆棱组油气藏成藏期次研究     

张庆飞  郭巍  丁鸿儒  李文强  杨绪海  张丛  刘孟骐 《世界地质》2017,36(2):552

对鸡西盆地城子河组、穆棱组岩石薄片进行显微镜下观察,挑选包裹体发育的样品切制包裹体薄片,在冷热台上开展流体包裹体均一温度测试,结合鸡西盆地的埋藏史和热史,探讨研究区城子河组、穆棱组的油气运移期次以及成藏时间。研究结果表明,研究区发生过两期四个幕次的油气运移事件,可划分为80~77 Ma和45~38 Ma两个期次,其中,城子河组有过三幕油气运移,充注时间分别为80 Ma、45 Ma及38 Ma,穆棱组在77 Ma发生过一幕油气充注。本次研究结果与鸡西盆地经历的两次构造运动相吻合:即(1)库拉板块(活动期120~65 Ma)对中国大陆边缘作用影响;(2)始新世—渐新世,约40 Ma的喜山早期运动,每次构造运动都伴随着油气运聚事件。  相似文献   

柴达木盆地西部大浪滩140 ka以来沉积特征与古环境   总被引：5，自引：0，他引：5  

侯献华  郑绵平  张成君  施林峰  王有德 《地质学报》2010,84(11):1623-1630

文章选取柴达木盆地西部大浪滩盐湖沉积中心的钻孔岩芯为研究对象,通过U系年代学研究,建立了该地区140kaBP以来的湖相地层沉积序列。从沉积特征来看,期间共经历了8次成盐期和6次淡化期,成盐期沉积的主要矿物为石盐、石膏、芒硝和白钠镁矾。淡化阶段主要矿物为粘土(伊利石占绝大多数,次为绿泥石和高岭石)、碳酸盐(方解石和白云石为主)和石英长石。对该时段碳氧同位素分析显示,140～113kaBP(92～84m),同末次间冰期的演化阶段(5e)有着很好的对应关系;113～93kaBP(84～78m)(5d),从碳同位素组成特征看,该阶段也有多次气候的颤动发生,在78～80m层段,有近2m厚的中粗粒芒硝,其为冷相矿物,这说明该阶段水体温度变化频繁;此外,93～87kaBP(78～74.6m)、87～79.5kaBP(74.6～67.5m)、79.5～76kaBP(67.5～63.5m)也都分别对应着末次间冰期后的5c、5b、5a三个阶段。76～72kaBP(60～64m)(MIS4),氧同位素组成快速偏重(-4‰～-8‰(PDB)),温度下降,水体明显咸化;72～30kaBP(60～16m)(MIS3),总体碳氧同位素组成偏重,代表干凉的古气候环境,期间有两次成盐期,代表了冷干时段;30～14kaBP(16～0m)(MIS2),氧同位素组成明显偏重,代表了末次盛冰期的到来,进而结束了湖泊水体沉积。  相似文献   

现代海底热水活动的系统性研究及其科学意义     

付伟  周永章  杨志军  张澄博  杨小强  何俊国  杨海生  罗春科 《地球科学进展》2005,20(1):81-088

现代海底热水活动是当前地球系统科学研究的一个重要组成部分，它是研究海底地质作用体系中的一个关键环节。海底的构造作用、岩浆活动等因素制约了热水循环的发育和活动规律，而热水活动又直接或间接地产生了一些地质效应，如海底的热水喷流成岩成矿效应，此外它还与海底的热能输导与转化、海洋化学组分特征、海洋生命和生命起源等现象有着密切的成因联系。开展现代海底热水活动的系统性研究，应注重将热水循环的内部动力学机制和热水活动所引发的外部环境效应相结合，为此我们把它初步展开为：热水循环的空间组构研究、热量输导作用研究、热水流体的化学成分研究、热水活动与极端生命的关系研究以及热水活动的生命周期研究等 5个方面，分别解析其内部特征以及引发的环境效应。最后初步探讨了开展海底热水活动的系统性研究的科学意义。  相似文献   

On the minimum of vertical seismic noise near 3 mHz     

W. Zürn  E. Wielandt 《Geophysical Journal International》2007,168(2):647-658

  相似文献   

从史料记载看中国历史时期海面波动   总被引：5，自引：0，他引：5  

王文  谢志仁 《地球科学进展》2001,16(2):272-278

广泛采用文字类海面变化“代用资料”是历史时期小尺度海面波动研究的重要手段，将史籍中有关海面波动的记载与考古学和沉积地层学证据相结合进行综合分析，可以初步认定：我国历史时期2ka年来，西汉至两晋为相对高海面时期（西汉晚期为显著高海面时期）；晋末至隋末为相对低海面时期，唐至南宋为相对高海面时期，尤其是8世纪，11世纪后期至13世纪初期出现显著高海面，而其间的唐末至五代，南宋后期至元初曾出现过海面下降；元明清时期总体为相对低海面时期，但在元中后期至明初，16世纪上半叶，17世纪末至18世纪初分别出现几次相对高海面。  相似文献   

北京西山的冰缘期和更新世自然环境   总被引：8，自引：1，他引：8  

郭旭东  严富华 《冰川冻土》1991,13(2):159-167

  相似文献   

Bedload entrainment,travel lengths,step lengths,rest periods—studied with passive (iron,magnetic) and active (radio) tracer techniques     

Karl-Heinz Schmidt  Peter Ergenzinger 《地球表面变化过程与地形》1992,17(2):147-165

This paper reports results from bedload transport investigations with active (radio) and passive (iron, magnetic) tracers in the Lainbach, a step-pool mountain river, in Bavaria, Southern Germany. The spatial distributions of the iron tracers after flood events can be best described by exponential or Gamma distributions. There is some indication of a tendency of size-selective transport of the iron tracers, but there is also a considerable amount of scatter in the correlations between weight (size) and travel length owing to the masking influence of other variables, such as the shape of the particles and different positions in the river bed. The experiments with artificial magnetic tracers showed that elongated pebbles (rods) had the longest mean transport distance, platy ones (discs) remained relatively close to the starting points. The particles from the pool showed the greatest transport lengths and a 100 per cent chance of being eroded. The Pebble Transmitter System (PETSY) consists of transmitters implanted into individual pebbles, a computerized receiver, a stationary antenna system with an antenna switchboard, and a data logging system. The particles do not move continuously but in a series of transport steps and non-movement intervals. A single value for a given size-class is not adequate to describe the critical conditions of entrainment under natural circumstances. A probability approach is much more suitable. The critical unit discharges (total discharge divided by active channel width) along the measuring reach are dependent on river bed morphology. In the steps bedload needs higher unit discharges to be entrained. Once entrained, the transport of bedload is stochastic in nature and the single particle transport is controlled by the step lengths and the duration of rest periods. The distributions of both parameters can be approximated by exponential functions. Applying the stochastic concept proposed by Einstein the mean values of the random variables [step length] and [duration of rest period] measured with the PETSY technique were used for the simulation of spatial distributions of bedload particles from point sources. More field and laboratory data are needed to include varying flow and roughness conditions with tracers representing different particle characteristics.  相似文献