共查询到20条相似文献，搜索用时 991 毫秒
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《技术与市场》2007,(1):23
当前现代化的航天、航空、汽车、机械、电子、民用建筑、化工等行业迫切要求具备很高的力学性能及耐热、耐磨、耐化学性能的材料.因此高分子材料发展的一个重要方向就是通过对现有聚合物进行物理和化学改性,使其进一步高性能化、结构化、工程化.北京化工大学研制的聚氯乙烯合金是通过挤出机的力学、化学作用及接枝、复合技术使聚氯乙烯塑料工程化,成为物理性能可与ABS相比拟的新材料.聚氯乙烯合金具有高流动性、高韧性,完全可以代替ABS注塑计算机、电视机、冰箱、照相机、仪表等外壳.聚氯乙烯合金还具有良好的耐寒性,可制作各种规格的异型材,包括门窗、上水管道等.产品市场前景好,具有很强的竞争力,有很好的经济效益和社会效益. 相似文献
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丹妮 《绿色中国(A版)》2008,(22)
在滇、桂、黔三省(区)结合部,有一片美丽而神秘的地方——罗平。去那里旅游不仅可以欣赏气势雄伟的瀑布群落、幽深险峻的峡谷、挺拔秀丽的峰丛、独特的地貌奇观、苍莽的林海、溢彩流金的油菜花海、蜿蜒曲折的河流、玲珑剔透的滩跌、碧绿如玉的湖泊构成的一道道靓丽的自然风景,还能看到丰富的文物古迹、感受古朴浓郁的布依风情、品尝许多美味佳肴,难怪明代大旅行家、地理学家徐霞客游览后写下罗平著名迤东的赞叹。 相似文献
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分别从海南省的三亚、文昌、琼山、广西的防城,广东省的雷州、廉江和深圳采集木榄胚轴,同时种植在深圳湾作种源试验。通过4a的试验表明,7种种源间的成活率、树高、地径和单株生物量的差异达到显著或极显著水平,其中以琼山种源表现最佳,其成活率、树高、地径和生物量分别为90.0%、1.54m、4.97cm、1.358kg,比表现最差的文昌种源分别提高17.8%、17.3%、12.2%、55.9%,比本地的深圳种源分别提高5.5%、18.2%、9.0%、6.1%。根据种源综合评定结果,各种源的优劣排列顺序为：琼山、廉江、深圳、三亚、防城、雷州、文昌。鉴于文昌、雷州种源在深圳湾适应性差,不宜在本地区种植推广。 相似文献
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前景看好的高价值树种——麻疯树 总被引：2，自引：0，他引：2
麻疯树,又名膏桐、小桐子、黑皂树等,属大戟科落叶灌木或小乔木,可以生长在荒山、荒地等贫瘠的土地上,是一种耐干旱、耐贫瘠的油料植物,主要分布在我国云南、贵州、四川、广东、广西、福建、海南等省海拔300～1600米的荒山、干热河谷地区. 相似文献
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【目的】为宁夏红枣的产地溯源提供参考。【方法】采集了宁夏灵武、中宁、同心3个产地共88份红枣样品,采用电感耦合等离子体质谱方法（ICP-MS）测定了红枣样品中36种矿物元素的含量,结合方差分析和主成分分析方法,筛选有效的溯源指标,采用Fisher判别分析方法和正交-偏最小二乘法判别分析方法（OPLS-DA）建立宁夏红枣产地的判别模型。【结果】灵武、中宁、同心3个产地红枣样品的36种矿物元素中有27种矿物元素含量存在显著差异。经过主成分分析,从36种矿物元素中提取出10个主成分,代表了总指标76.359%的信息,筛选出Na、Zn、Mn、B、Cr、Co、Cd、Ce、Dy、Ni、Nb、Rb、Y、Nd、Pr、Sr、Li、Hg、Hf、Pd、Sb、Ga、Mo、W、Pb、Sn共26种红枣的特征矿物元素。经Fisher判别分析,确定了Mn、Pd、Sn、Sr、Hg、Co、Cu、B、Ba、As共10种矿物元素为红枣的有效溯源指标,构建宁夏红枣产地的Fisher判别模型,经回代和交叉检验,模型的整体正确判别率分别为100%和98.9%。采用OPLS-DA判别分析方法建立的判别模型的整体正确判别率为100%。... 相似文献
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Assessment of standing wood and fiber quality using ground and airborne laser scanning: A review 总被引：1，自引：0，他引：1
Martin van Leeuwen Thomas HilkerNicholas C. Coops Gordon FrazerMichael A. Wulder Glenn J. NewnhamDarius S. Culvenor 《Forest Ecology and Management》2011,261(9):1467-1478
Accurate information on the wood-quality characteristics of standing timber and logs is needed to optimize the forest production value chain and to assess the potential of forest resources to meet other services. Physical and chemical characteristics of wood vary with both tree and site characteristics. At the tree scale, crown development, stem shape and taper, branch size and branch location, knot size, type and placement, and age all influence wood properties. More broadly, at the stand level, stocking density, moisture, nutrient availability, climate, competition, disturbance, and stand age have also been identified as key determinants of wood quality. Such information is often captured in polygon based forest inventory data. Other terrain-related spatial information, such as elevation, slope and aspect, can improve assessments of site conditions and limitations upon plant growth which impact wood quality. Light Detection And Ranging (LiDAR) is an emerging technology, which directly measures the three-dimensional structure of forest canopies using ground or airborne laser instruments, and can provide highly accurate information on individual-tree and stand-level forest structure. In this paper, we explore the potential of LiDAR and other geospatial information sources to model and predict wood quality based on individual-tree and stand structural metrics. We identify a number of key wood quality attributes (i.e., basic wood density, cell perimeter, cell coarseness, fiber length, and microfibril angle) and demonstrate links between these properties and forest structure and site attributes. Finally, the potential for using LiDAR in combination with other geospatial information sources to predict wood quality in standing timber is discussed. 相似文献
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Jochen Schöngart Florian Wittmann Martin Worbes Maria Teresa Fernandez Piedade Hans-Jürgen Krambeck Wolfgang Johannes Junk 《Annals of Forest Science》2007,64(6):657-664
Ficus insipida Willd. (Moraceae) is a fast growing tree species of early successional stages in the Amazonian nutrient-rich white-water floodplains (várzea). The species is one of the most economically important low-density wood species in the community-based forest management project in the Mamirauá Sustainable Development Reserve (MSDR) in Central Amazonia, where timber species are managed using a polycyclic selection system with a minimum logging diameter (MLD) of 50 cm and a cutting cycle of 25 years. In this study we analyze the floristic composition, stand structure and forest regeneration of a natural 20 year-old stand at an early successional stage and we model tree growth of diameter, height and volume of F. inspida based on tree-ring analysis to define management criteria. The volume growth model indicates that the preferred period for logging should be at a tree age of 17 years when the current annual volume increment peaks. This age corresponds to a diameter of 55 cm, which would be an appropriate MLD. 相似文献
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小径原木是当今世界上主要的木材资源之一,各国均在积极开发利用。文内着重介绍了林业发达国家在研究小径原木的材性特征和主要产品加工工艺特点等方面所取得的成果和经验。 相似文献
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浅析山河屯林业局天然次生林现状及管理措施 总被引：1，自引：0，他引：1
天然次生林面积占黑龙江省山河屯林业局总经营面积的87.3%多,这部分林分整体上树种结构不合理、林相残破、经济利用价值较低而且改造难度较大。但是,并不等于说这部分林分没有较高的利用价值就放弃它,当前应本着珍惜资源的态度,对其加强科学经营管护和改造力度,重经营少砍伐,同时由于林木生长周期长,这部分林分在短期内很难恢复和发展起来,因此应积极发展多元化经济,在现有资源条件下提高木材的利用率,提升木材精深加工水平,积极开发药业、山产品、苗木花卉、旅游等产业,缓解木材生产的压力,繁荣和发展林区经济。 相似文献
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Jori Uusitalo Olli Ylhäisi Hannu Rummukainen Marika Makkonen 《Scandinavian Journal of Forest Research》2018,33(5):475-483
Knot properties have a profound influence on the suitability of wood for many wood products leading to significant value differences between different quality grades. It would therefore be rather advantageous to maximise the volume of good quality timber attained from the logs. The objective of this study was to assess how well A-quality lumber of Scots pine derived from log tomography features can be predicted with characteristics measured prior to or concurrently with the logging operation. The study is based on field experiments and X-ray scanning of 204 stems from southern Finland in 2014. We employed mixed logistic regression techniques to model the relationship between the main stem characteristics and probability of A-quality lumber. From the tree characteristics that can be measured or detected from standing trees, the height from the ground level to the lowest dead branch was found to be the best predictor of A-quality lumber. From the characteristics that could, at least in theory, be detected and measured at the moment of harvest, early growth rate and size of tree were found to be the best combination for predicting the probability of A-class quality. 相似文献
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以广西黄冕林场的几个桉树树种为研究对象,对比分析不同树种生长、立木材性以及林分密度对其影响。结果表明：各树种的生长（树高、胸径、单株材积、冠幅、树皮厚度）和材性（立木Pilodyn值、应力波波速、基本密度）性状均差异显著。比较3种不同林分密度的邓恩桉发现,林分密度对其生长、材质形成等产生显著影响,适宜的林分密度有利于林木生长和材性形成。对各性状采用主成分分析法进行了树种评价,结果表明：巨桉林木生长量大,大花序桉和本沁桉生长量相对较少,但木材材质相近,表现为坚硬,而粗皮桉、柳桉、邓恩桉均低于对照尾巨桉。从林木生长、立木材性方面看,适合于该地区发展的树种有巨桉、大花序桉和本沁桉,其中巨桉最适宜。 相似文献
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