共查询到20条相似文献,搜索用时 15 毫秒
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小蠹科害虫化学信息物质及其对侵害寄主等行为的影响 总被引:1,自引:0,他引:1
在综合大量国内外研究成果的基础上,就松树寄主气味、非寄主气味、小蠹虫信息素以及其他化学信息物质对调控小蠹科害虫侵袭寄主林木等的行为,作了系统详细的论述。 相似文献
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黑龙江森林火灾初次扑救派出人员数量模拟与分析 总被引:1,自引:0,他引:1
通过问卷调查收集了黑龙江省若干基层扑火指挥员对不同火场情景时的初次扑救派出人员数量 ,据此通过二次线性回归分别建立了根据火场情况 (火场面积、风级和到火场所需时间 )模拟森林火灾扑救初次派出人员数量的非线性模型 ,并对有关影响因素进行了分析。结果表明 ,(1)所建立的多元非线性模型能够较好地模拟派出人员数量 ;(2 )根据各地情况分别做出的模型模拟效果好 ,而以地区或省为单位进行模拟效果不好 ;(3)在火场面积小于 2hm2 时 ,多数人将风力看作是影响初次派出人员数量的首要因素 ,其次是到达火场所需时间 ,最后是火场面积 ;(4)随着指挥员工作时间的增长 ,模型中赋予到火场所需时间的权重增加 ,对到达火场所需时间越重视。 相似文献
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王培芝 《中南林业科技大学学报(自然科学版)》1988,(1)
本文根据平面应力状态的解析式,推导出了一种判别最大应力极值所在方向的简捷方法。本法除了具有无须作图和较为准确的特点外,还适用于对平面应变状态中最大应变极值方向和平面图形中最大惯矩极值方向进行判别。 相似文献
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结合无粘结预应力技术在高层结构中的应用,对设计计算基本原理、步骤到参数选择、内力分析等问题进行了较详细的阐述,可供业内人士参考。 相似文献
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本文对林用门式起重机主要部分杆件进行了应力分析,并利用应变片电测法对其应力进行了测定。结果表明,实测应力与计算应力相近,实测应力小于计算应力的居多数,个别杆件的实测应力略大于计算应力。 相似文献
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《Scandinavian Journal of Forest Research》2012,27(1):39-48
Stemflow water acidifies the soil in beech stands impacted by atmospheric deposition. To investigate whether the soil recovers from acidification, stemflow was experimentally removed. A horizon material was sampled at a distance of 10 - 250 cm from the stems. Before the onset of the experiment, there were stemflow - induced gradients in the saturation of exchange sites with K+, H+ and Na+ that were larger near the stems, while the pHKCl, the cation - exchange capacity, and the saturation with Ca2+, Mg2+ and Mn2+ were smaller. After 8 yrs of recovery, the pHKCl and the saturation with Ca2+ and Mg2+ had increased close to the stems, while the saturation with Na+, H+, Mn2+ and 2+ and the C/N ratio had decreased. With some exceptions, e.g. base saturation, the recovery was not complete after 8 yrs. Soil far from stems had also changed similarly, probably because of the ongoing decrease in overall deposition in southern Sweden. 相似文献
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《Scandinavian Journal of Forest Research》2012,27(1-4):351-357
The attack density and brood production of Tomicus piniperda (L.) (Col., Scolytidae) were recorded on stems of Pinus sylvestris L. felled in southern, central, and northern Sweden before, during, and after the spring flight period in 1977 and 1978. The study sites were adjacent to stands clear‐felled during the last or the previous winter. The attack density (i.e., the number of egg galleries per m2 inner bark area) varied considerably between localities and years. At all sites high attack densities were recorded in trees felled before or soon after the flight commencement, whereas few attacks occurred in trees felled in late May or later. The availability of brood material did not affect the seasonal attack pattern in any consistent way. The brood production varied from zero to more than 900 individuals per m2. 相似文献