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931.
水分胁迫对栓皮栎幼苗生理特性及生长的影响 总被引:11,自引:0,他引:11
通过盆栽实验,研究了在不同的水分条件下栓皮栎幼苗生理特性的变化和苗木生长量的变化。研究表明,在水分胁迫初期,随土壤含水量的降低,栓皮栎叶片的净光合速率、蒸腾速率下降,而水分利用效率提高。在水分胁迫末期,由于长期的干旱胁迫,水分条件最差的一组苗木已干枯死亡,土壤含水量从38.123%下降到20.323%时,净光合速率和蒸腾速率均下降,水分利用效率也下降。随着土壤含水量的降低,苗高、地径和生物量均有下降的趋势,其中生物量下降的幅度最大。 相似文献
932.
生态旅游作为旅游开发的一大热点,在开发中面临着如何丰富、深化其内涵的问题.我国是一个竹资源丰富的国家,该文就竹资源在发展生态旅游中的价值从竹子的观赏造景功能、文化承载功能、旅游商品开发价值等方面进行了探讨. 相似文献
933.
Technical change is developing rapidly in some parts of the forest sector, especially in the pulp and paper industry where wood fiber is being substituted by waste paper. In forest sector models, the processing of wood and other input into products is frequently represented by activity analysis (input–output). In this context, technical change translates in changes over time of the input–output (I–O) coefficients and of the manufacturing cost (labor, capital, and materials, excluding wood and fiber). In the case of the global forest products model, the I–O coefficients and the manufacturing costs are determined empirically from historical data, while correcting for possible reporting errors. The method consists of goal programming. The objective function is the sum of the weighted absolute value of the deviations from estimated and observed production in each country of interest. The constraints express the relationship between the multiple output (sawnwood, panels, pulp, paper) and input (wood, waste paper, other fiber) and prior knowledge on the limits of the I–O coefficients. The paper presents observed technical changes from 1993 to 2010 and projections to 2030 with their consequences for the global forest sector in terms of prices, production and consumption, value added, and carbon sequestration in forest biomass. 相似文献
934.
This paper took the upper-lower wide belt sander B229 with four-feet wide belts, manufactured in China, as the study target.
By means of framework dynamic design, we study its vibration characteristics by commencing from the place having horizontal
defects and used experimental modal analysis (EMA) and power spectrum density (PSD) to observe the sanding parts and the whole
machine, respectively. In the modal test, we mainly adopted the cross spots testing method to get the frequency response function
of the fixed spots to every excitation vibration spot, then applied the SISO frequency response function and the frequency
response function fitting method to identify and complete parameter recognition, respectively. The typical frequency response
function chart of the whole machine and its sanding parts, as well as its second-order mode charts of contacting roller, were
obtained. Through PSD analysis, we can get the amplitude-frequency spectrum and drive frequency.
Translated from Scientia Silvae Sinicae, 2005, 41(6): 132–137 [译自: 林业科学] 相似文献
935.
“なんだか”与“なんとなく”都是副词,在意义和用法上既有相同之处,也有不同之处。但是,在什么样的场合,其意义和用法相同,二者可以换用;在什么样的场合,其意义和用法又不尽相同,二者不能互换,却是一个十分复杂,难以掌握的问题。本文对这两个词在意义和用法上的异同做一探讨。 相似文献
936.
采用多年多点进行菇木多树种育苗造林试验,3年来共育苗11hm2,营造试验林20.8hm2,示范林68.5hm2,树种19个。试验结果表明,选用水稻田育苗,通过间苗补植等措施,使合格苗达80%以上;选择山坡谷地的土层深厚、肥沃湿润地段造林,其成活率达85.8%~98.3%2年生桤木幼树,平均树高3.93m,平均地径4.1cm。初步看出桤木、杜英、马褂木是良好的速生菇木树种。 相似文献
937.
938.
939.
940.
Populus tomento a was crossed with P. tremuloidis, P grandiden ata, P. lba × P. grandidentata and P. alba × Ulmus s . ta pumila in order to maintain its rapid growth and high wood quality and improve its resistance to cold. Two methods were used to increase the germination rate from 1.5% to 41.1% and the remaining rate from 1.7% to 44.2%. Forty crossing combinations were conducted and 2 744 hybrid seedlings were obtained. MX. t4 × P grandiden ata (G-1-58), MX3 × P. tremuloidis (T-44-60), MX2 × P. tremuloidis (l-13-87-37) and MX2 × (P. alba × P. grandidentata) were regarded as superior combinations after analysis and selection. Thirty seedlings of these combinations and 11 triploid seedlings identified by counting their chromosomes were selected as super plants. 相似文献