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21.
西藏日喀则流沙固定的几个问题 总被引:12,自引:5,他引:7
1995年首次在西藏日喀则进行固沙植物的引种试验,大多数中国内地固沙植物不适应该地的流动沙丘,沙面高温和生长季短是主要制约因素。沙木蓼和籽蒿表现最好;油蒿种子不能成熟,因此不能做后续植物;乡土植物砂生槐在播种当年出苗率低、生长缓慢,只能用做后期植物。在西藏日喀则,有效的植物固沙程序是:在保护措施(草方格沙障、砾石层)下,在流动沙丘上播种外来种沙木蓼、籽蒿和油蒿或移栽籽蒿,同时播种乡土植物砂生槐。在沙木蓼和籽蒿种群衰退、油蒿种群未衰退但不能靠天然下种自行更新时,砂生槐开始发挥固沙作用,并最终凭其适沙特性和长寿命接替先锋固沙植物有效地固定沙丘。选择乡土固沙植物应将重点放在蒿属和锦鸡儿属上。 相似文献
22.
Alexander V. Turbiner 《Astrophysics and Space Science》2007,308(1-4):267-277
Brief overview of one-two electron molecular systems made out of protons and/or α-particles in a strong magnetic field B≤4.414×1013 G is presented. A particular emphasis is given to the one-electron exotic ions H3++(pppe), He23+(α
α
e) and to two-electron ionsH3+(pppee), He2++(α
α
ee).
Quantitative studies in a strong magnetic field are very complicated technically. Novel approach to the few-electron Coulomb
systems in magnetic field, which provides accurate results, based on variational calculus with physically relevant trial functions
is briefly described.
相似文献
23.
The alien halophilous Artemia species, Artemia franciscana, was found in Chengkou Saltern and Yangkou Saltern of Shandong Province, P.R. China. Although the indigenous parthenogenetic
Artemia is detectable, the exotic species is dominant in both salterns. The cross-breeding tests between the exotic A. franciscana and 5 bisexual Artemia species were conducted. The results of hybridization and morphological observations on the exotic A. franciscana are briefly presented in this short communication. 相似文献
24.
YIN Zuowei LU Fengxiang CHEN Meihua Gemmological Institute China University of Geosciences Wuhan Hubei Earth Science Department China University of Geosciences Wuhan Hubei 《《地质学报》英文版》2005,79(5):654-661
1Introduction Due to its special properties and ubiquitous occurrence,zircon can be found in the crust,mantle,lunar rocks,meteorites,etc.And it is the ideal mineral to test the formation age of rocks(Xie et al.,2001).However,zircons are an exceptionally rare component of kimberlites.They have various sources and courses of formation.Zircons crystallized from kimberlitic magma are usually have large sizes and a maximum diameter of20mm was reported.Typically,they have low contents of U and Th,… 相似文献
25.
On the potential of plant species invasion influencing bio‐geomorphologic landscape formation in salt marshes
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Christian Schwarz Tom Ysebaert Wouter Vandenbruwaene Stijn Temmerman LiQuan Zhang Peter M. J. Herman 《地球表面变化过程与地形》2016,41(14):2047-2057
Species invasions are known to change biotic and abiotic ecosystem characteristics such as community structure, cycling of materials and dynamics of rivers. However, their ability to alter interactions between biotic and abiotic ecosystem components, in particular bio‐geomorphic feedbacks and the resulting landscape configuration in tidal wetlands, such as tidal channels have not yet been demonstrated. We studied the impact of altered bio‐geomorphic feedbacks on geomorphologic features (i.e. tidal wetland channels), by comparing proxies for channel network geometry (unchanneled flow lengths, fractal dimension) over time between non‐invaded and invaded salt marsh habitats. The non‐invaded habitats (the south of eastern Chongming Island, Yangtze estuary, China) show little change in network geometry over time with a tendency for an increased drainage density. The invaded site (salt marshes in the north of eastern Chongming Island invaded by the exotic plant species Spartina alterniflora) showed a decreasing tendency in channel drainage density throughout and after the species invasion. This suggests that species invasions might not only affect biotic ecosystem characteristics, but also their ability to change bio‐geomorphic feedback loops, potentially leading to changes in existing geomorphologic features and therefore landscape configuration. Our results further suggest that the species invasion also altered sediment composition. Based on observations we propose a mechanism explaining the change in channel drainage density by an alteration in plant properties. The physical and physiological characteristics of the invading species Spartina alterniflora clearly differ from the native species Scirpus mariqueter, inducing different bio‐geomorphic feedback loops leading to the observed change in salt marsh channel configuration. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
26.
André Padua Emilio Lanna Carla Zilberberg Paulo César de Paiva Michelle Klautau 《Marine Ecology》2013,34(1):56-61
Little is known about the recruitment and behaviour of sponge larvae, especially of the class Calcarea. The calcareous sponge Paraleucilla magna is very common in Southeast Brazil, where it is considered a cryptogenic species. This study quantified recruitment rates in shaded and illuminated habitats for 2 years in Rio de Janeiro, Brazil, and analyzed larval photoresponses of this species. Four structures, each containing a shaded and an illuminated surface, were exchanged every 3 months for 2 years. The number of recruits was quantified on each plate. In the laboratory, larvae of P. magna were placed in half‐shaded Petri dishes and the number of settlers in each side was counted after 24 h. Paraleucilla magna recruited continuously throughout the experiment. Recruits occurred in greater abundance on shaded surfaces than on illuminated surfaces, and the larvae were negatively phototactic in vitro. Despite the possible influence of other factors in the recruitment of sponges (such as sedimentation, competition and predation), the prevalence of P. magna in shaded habitats may also be related to larval choice. 相似文献
27.
28.
通过在加依尔地区中—上石炭统太勒古拉组发现的外来岩块,查清了该区泥盆纪和石炭纪化石共生的原因,为确定该地区地层时代提供了佐证,并对研究本区石炭系的形成环境及区域构造演化等均将有新的启示. 相似文献
29.
Stakeholders’ perceptions of the impacts of invasive exotic plant species in the Mediterranean region 总被引:1,自引:0,他引:1
Invasive species pose an increasing environmental problem across the globe, but to date socio-economic perspectives on this
problem have been limited. In this study stakeholder perceptions of the impacts of invasive exotic plant species on the islands
of Mallorca, Sardinia and Crete are examined through the use of semi-structured interviews, Likert scales and Contingent Valuation.
Results showed substantial concerns about the impact of invasive exotic plant species on the islands, particularly on Mallorca
where awareness of the issue has increased in recent times due to campaigns to eradicate terrestrial and aquatic invasive
plants. Not all perceptions are negative and several respondents suggest that a turnover in local species is an inherent part
of the sense of the place in the region. If the management of invasive exotic plant species in the Mediterranean region is
to improve then there is a need to raise awareness of the impact of invasive species amongst both the general public and professional
stakeholders. 相似文献
30.