首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   50篇
  免费   4篇
  国内免费   1篇
林业   39篇
综合类   16篇
  2022年   1篇
  2021年   3篇
  2020年   1篇
  2017年   2篇
  2016年   2篇
  2015年   4篇
  2013年   11篇
  2012年   5篇
  2011年   6篇
  2009年   4篇
  2007年   3篇
  2006年   1篇
  2005年   3篇
  2004年   2篇
  2003年   1篇
  2001年   3篇
  1998年   2篇
  1992年   1篇
排序方式: 共有55条查询结果,搜索用时 16 毫秒
1.
研究火力楠心材与边材的颜色和物理力学性质,为该树种木材的合理开发和利用提供参考。采用CIE Lab颜色系统表征木材的颜色参数(明度指数L*、红绿轴色品指数a*、黄蓝轴色品指数b*);按照国家标准测量木材的物理性质(密度、干缩性、湿胀性)和力学性质(顺纹抗压强度、横纹抗压强度、抗弯强度、抗弯弹性模量、顺纹抗剪强度、硬度、冲击韧性、顺纹抗拉强度、抗劈力、握钉力)。结果表明,火力楠心材的L*a*b*均小于边材,表明心材的颜色偏向黑色的程度更大,而偏向红色和黄色的程度更小,整体颜色更加暗深;火力楠心材与边材的总色差属人视觉感觉差异“可察觉”。火力楠心材的密度小于边材,二者密度均属中等;心材的差异干缩大于边材,二者气干干缩的不均匀性均属小;心材的体积干缩系数小于边材,二者干缩性均属很小。火力楠边材的吸水增重率大于心材,表明边材的渗透性优于心材。火力楠边材的硬度、冲击韧性、抗劈力和握钉力大于心材,而其余力学指标小于心材。火力楠心材和边材的顺纹抗压强度、抗弯强度、顺纹抗剪强度、端面硬度和冲击韧性,均属木材各项力学指标品质分级的中等及以上水平。火力楠心材的综合强度和综合品质系数均大于边材,二者均分别属高强度和强重比很高。  相似文献   
2.
黑木相思株内木材基本材性变化与树龄关系的研究   总被引:1,自引:0,他引:1  
对不同树龄和径向位置黑木相思木材的物理和主要力学性质测定研究表明:黑木相思株内边材、心材密度和主要力学性质随着树龄的增大而增大,径向和弦向的体积干缩率随着树龄的增大而减小;相同树龄黑木相思的边材密度和力学性能比心材小,干缩率比心材大.因此,在利用黑木相思时应对树龄、心边材径向位置加以特别考虑.  相似文献   
3.
以速生杨木的边/心材单板为研究对象,对其进行水热密实化处理,通过单因素试验方法,分别研究了加压温度和加压压力对杨木边/心材单板的压缩率、气干24和48 h的厚度回弹率的影响,初步探讨了各个因素的作用机理.研究发现:各因素水平下,杨木边/心材单板的压缩率和厚度回弹率均呈现出一定的规律性,心材单板的压缩率高于边材单板,但厚度回弹率低于边材单板,且各因素的作用机理有所差异.边/心材单板水热密实化处理的较佳条件均为:加压温度150℃,加压压力5 MPa.  相似文献   
4.
心材形成机理与人工促进研究进展   总被引:5,自引:1,他引:4  
珍贵树种心材供不应求,主要归因于心材自然形成缓慢。研究如何人为地促进心材形成意义重大,但国内外相关研究综述还未见报道。文中在介绍心材形成的变化过程和主要机理假说的基础上,系统地总结生长调节剂、接种菌类、外源气体和其他抚育措施等人工促进心材形成的主要研究技术及成果,并结合课题组多年的研究提出了存在的不足与展望,以期为今后心材形成机理和人工促进心材形成的相关研究提供参考。  相似文献   
5.
Abstract

Thermal modification has been developed for an industrial method to increase the biological durability and dimensional stability of wood. In this study the effects of thermal modification on resistance against soft- and brown-rot fungi of sapwood and heartwood of Scots pine and Norway spruce were investigated using laboratory test methods. Natural durability against soft-rot microfungi was determined according to CEN/TS 15083-2 (2005) by measuring the mass loss and modulus of elasticity (MOE) loss after an incubation period of 32 weeks. An agar block test was used to determine the resistance to two brown-rot fungi using two exposure periods. In particular, the effect of the temperature of the thermal modification was studied, and the results were compared with results from untreated pine and spruce samples. The decay resistance of reference untreated wood species (Siberian larch, bangkirai, merbau and western red cedar) was also studied in the soft-rot test. On average, the soft-rot and brown-rot tests gave quite similar results. In general, the untreated heartwood of pine was more resistant to decay than the sapwood of pine and the sapwood and heartwood of spruce. Thermal modification increased the biological durability of all samples. The effect of thermal modification seemed to be most effective within pine heartwood. However, very high thermal modification temperature over 230°C was needed to reach resistance against decay comparable with the durability classes of “durable” or “very durable” in the soft-rot test. The brown-rot test gave slightly better durability classes than the soft-rot test. The most durable untreated wood species was merbau, the durability of which could be evaluated as equal to the durability class “moderately durable”.  相似文献   
6.
Abstract

Thermal modification at elevated temperatures changes the chemical, biological and physical properties of wood. In this study, the effects of the level of thermal modification and the decay exposure (natural durability against soft-rot microfungi) on the modulus of elasticity (MOE) and modulus of rupture (MOR) of the sapwood and heartwood of Scots pine and Norway spruce were investigated with a static bending test using a central loading method in accordance with EN 408 (1995). The results were compared with four reference wood species: Siberian larch, bangkirai, merbau and western red cedar. In general, both the thermal modification and the decay exposure decreased the strength properties. On average, the higher the thermal modification temperature, the more MOE and MOR decreased with unexposed samples and increased with decayed samples, compared with the unmodified reference samples. The strength of bangkirai was least reduced in the group of the reference wood species. On average, untreated wood material will be stronger than thermally modified wood material until wood is exposed to decaying fungi. Thermal modification at high temperatures over 210°C very effectively prevents wood from decay; however, strength properties are then affected by thermal modification itself.  相似文献   
7.
Variation of sapwood thickness in terms of a linear measurement and a growth ring count with reference to the age was studied in dominant and suppressed Norway spruce trees. In the trees of both dominance classes the sapwood thickness increased in absolute terms, while its relative portion decreased with the age of the trees growing. Great differences were found in sapwood thickness between dominant and suppressed trees in linear measurements but not in the number of sapwood rings or the rate of the heartwood formation. The number of sapwood growth rings reached 40 in old trees. The index of vigour differed considerably in dominant and suppressed trees.  相似文献   
8.
本文是以丰林保护区阔叶红松成过熟林木为研究对象,通过对红松株数,无腐率、心腐率、边腐率统计结果表明:心腐率随根径的增大而增加,且以林分类型为主要因子而转移,林分中红松成过熟林木无腐朽率为19.4%、心腐率为75.3%、边腐率为5.3%.  相似文献   
9.
Water stress and fire disturbance can directly impact stand structure, biomass and composition by causing mortality and influencing competitive interactions among trees. However, open eucalypt forests of southwest Australia are highly resilient to fire and drought and may respond differently to increased fire frequency and aridity than forests dominated by non-eucalypt species. We measured the variation in stem density, basal area, stand biomass, sapwood area, leaf area and litterfall across 16 mixed jarrah (Eucalyptus marginata) and marri (Corymbia calophylla) forest stands along an aridity gradient in southwest Australia that had variable fire histories. Fire frequency was defined as the total number of fires over a ∼30-year period and aridity as the ratio of potential evapotranspiration to annual precipitation. Total stand biomass and sapwood area were predicted from diameter at breast height of individual jarrah and marri trees using allometric equations. Leaf area was estimated using digital cover photography. More arid and frequently burnt stands had higher stem density, especially of smaller trees, which were mainly jarrah. Overall, both standing biomass and leaf area decreased at more arid sites, while sapwood area was largely unaffected by aridity, suggesting that these stands respond to increased water limitation by decreasing their leaf area relative to their sapwood area. Biomass of marri was reduced at more arid and, to a lesser extent, at more frequently burnt stands. However, total stand biomass (jarrah and marri) and leaf area index did not vary with fire frequency, suggesting that less marri biomass (due to slower growth rates, higher mortality or less recruitment) was compensated by an increase in the density of jarrah trees (regeneration). We conclude that increased fire and drought shift tree species composition towards more fire-resistant species and result in denser stands of smaller trees. In contrast, total stand biomass declines with increasing aridity, but has no association with fire frequency.  相似文献   
10.
将原子力显微镜技术应用于木陶瓷分析,观测了大青杨木材和酚醛树脂炭化前后样品表面的微观形态.结果表明,通过原子力显微镜技术,可以清晰地观察到大青杨木材表面呈波纹状排列有序的纤维物质,波纹峰谷间水平距离390.63nm,垂直距离14.745nm.炭化后该结构消失,样品的粗糙度大大增加,均方根粗糙度由炭化前的4.487nm增加到炭化后的68.147nm.未炭化酚醛树脂因固化时水分的逸出,留下类似火山口状的峰谷,谷宽437.60nm,谷深22.202nm.炭化后该结构完全消失,样品的均方根粗糙度由炭化前的4.612nm增加到50.446nm.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号