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排序方式: 共有238条查询结果,搜索用时 31 毫秒
21.
The Himalayan Yew (Taxus baccata subsp, wallichiana) is an endangered native high value medicinal plant of the Himalayan Region. The several medicinal properties of the bark and leaves of this species have increased its risk of extinction due to pressures for utilization. It is also subjected to harvest for fuelwood. The species does not regenerate well from seed and that is another risk factor. The objective of this research was to investigate the population ecology of the species as a foundation for its conservation. Six forest communities in the Khokhan Wildlife Sanctuary where the species is present were sampled. The abundance of the species, impacts of harvesting and its current regeneration patterns indicate that it may soon be extirpated from the Sanctuary. A plan for conserving the remaining sub-populations is presented. It could provide a template for conservation in other locations where the species is at risk. 相似文献
22.
A group of coenocytic marine algae differs from higher plants,whose totipotency depends on an intact cell(or protoplast).Instead,this alga is able to aggregate its extruded protoplasm in sea water and generate new mature individuals.It is thought that lectins play a key role in the aggregation process.We purified a lectin associated with the aggregation of cell organelles in Bryopsis hypnoides.The lectin was ca.27 kDa with a pI between pH 5 and pH 6.The absence of carbohydrate suggested that the lectin was ... 相似文献
23.
Natural assemblages of marine bacteria were chosen in a batch culture experiments. The impact of varying nitrogen substrate concentrations and the substrate C:N ratios (C:NS) on the bacterial C:N ratio (C:NB), the bacterial growth efficiency (BGE) and ammonium regeneration was mainly examined. The C:NS ratios varied from 5:1 (carbon limitation) to 40:1 (nitrogen limitation) with varying combinations of glucose and NO3-. The C:NB ratio had positive relationship with the C:NS ratio (r=0.93, n=8), whose value was 3.77 when the C:NS ratio was 5:1 but increased to 6.47 when the C:NS ratio was 40:1. These results indicate that the C:NB ratio is a potential diagnostic tool for determining the bacterial growth in natural waters controlled by either, carbon or nitrogen. BGE decreased with the declining nitrate concentration and negatively related to C:Ns (r=-0.51, n=8). The average value of BGE was 0.20. This value was a little lower than other reports, which could be induced by the nitrogen source used in our experiments. Finally, regeneration time of ammonium delayed with the increasing C:NS ratio, which indicates that there were different metabolism mechanisms when bacterial growth was limited by carbon source and nitrogen source. 相似文献
24.
土地是人类赖以生存的基础,是工业生产活动最基本的生产要素之一。十分珍惜、合理利用每一寸土地是我国的基本国策,也是人类应尽的义务,浪费每一寸土地都是在犯罪。当前,土地资源的开发、保护、管理已纳入各级政府的重要日程,对土地资源的合理利用已成为社会广泛关注的焦点。就煤炭工业城市而言,采煤后沉陷区内废弃和闲置的土地如何进行再生利用,如何变废为宝,造福子孙,成为我们不容忽视的重大课题。解决好这一难题,既是促进地方经济发展的迫切需要,又是建设资源节约和环境友好型社会的必然要求。 相似文献
25.
初步研究了细基江蓠繁枝变种(G. tenuistipitata var. liui)和细基江蓠(G. tenuistipitata)切段培养的适宜培养基及其切段的再生特点。在此基础上,还研究了几种植物生长调节剂对江蓠藻体切段再生的影响。研究表明,江蓠藻体在改良PES培养基中生长良好。两种藻体的外皮层细胞均可产生长成新枝的生长点,并且表现出相同的再生极性。无论细基江蓠繁枝变种还是细基江蓠的切段都是在形态学上端切口处产生新枝,下端不再生;带分枝的切段,其分枝断口处亦可再生新枝。适宜的植物生长调节剂可明显促进藻体芽的产生和生长。1 m g/ LBA 明显促进细基江蓠繁枝变种切段的再生,2 m g/ L BA+ 0.5 m g/L NAA 显著促进细基江蓠切段的再生 相似文献
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基于交通管控效应的中国COVID-19疫情扩散的时空特征及其危险性 总被引:1,自引:0,他引:1
基于中国各级卫健委公布的疫情数据和全国列车数据,结合交通管控措施解析了中国COVID-19疫情扩散的时空特征和危害性,以及湖北“封省”对全国铁路系统的影响,结果发现:1)中国的疫情增长过程高度符合Logistic分布;空间上由湖北往东、南方向蔓延强度较大,各省内部疫情较为严重的地区通常为省会或经济发达城市。基于交通管控对疫情扩散的扰动,揭示了COVID-19的平均潜伏期约为4 d;并基于此测算了疫情的基本再生指数(R0),结果显示:R0整体上呈波动下降趋势,截至2020-04-08全国各地区的R0均趋于1;湖北以外的愈亡比远高于湖北,表明在医疗资源充足的情况下,疫情的危险性可以大幅降低。2)通过湖北“封省”管控前后的铁路网络对比得出,湖北“封省”措施对中心性较高的城市影响较大,尤其是长三角地区,对中心性较低的城市影响微弱;此外,“封省”措施对全国铁路网络整体连通性不会产生根本性的影响。 相似文献
29.
内衬非开挖管道修复技术是在不开挖情况下,利用原管位资源,采取相关技术在现有管道内安装内衬的方式使管道获得再生,可以重新获得30~50年的使用寿命.对内衬法非开挖管道修复技术的工艺原理进行了介绍,对其应用前景进行了分析. 相似文献
30.
The reproductive ecology of the mudskipper Boleophthalmus pectinirostris was investigated during the spawning season in the Funing Bay, Fujian, China. The fish burrows were basically Y-shaped and had two openings onto the mudflats. Part of the intersection at the center of the burrow was dilated to form a "spawning chamber". The dissolved oxygen concentrations (0.40~0.65 mg/dm3)of water 15 cm deep inside the burrows were much lower than those (5.96~6.19 mg/dm3) of intertidal pool water. Water temperatures inside the burrows were much lower than those of intertidal pools. Field investigations indicated that eggs were laid on the inner wall and ceiling of the spawning chamber by means of filamentous attachments, and a male stayed inside the burrows to guard it. Field investigations also suggested that fish of both sexes constructed mud burrows by themselves but that the spawning chamber was made only in the male burrow. The male attracted a female to his burrow for mating and spawning. There was no water in the spawning chamber, and thus the eggs were exposed to the air in the chamber. Changes in spawning readiness and gonadosomatic index indicated that synchronization of spawning was related to the semi-lunar periodicity, and this is the first report of this relationship in the mudskippers. 相似文献