四川省开县山区农业气候资源的质量评价

在确定了山区农业气候资源质量综合评价原则的基础上,建立评价的指标体系和评价标准,进而提出综合指数、模糊判别、希尔伯特空间距离系数等3种评价方法.本文以四川省开县为例,给出了农业气候资源环境质量的定量评价结果,并对3种评价方法进行了讨论和比较.     

夹具与槽口距离对胶合板强度测定结果的影响

通过试验,研究了胶合板胶合强度检测试验中夹具与试件槽口的距离对胶合板胶合强度的影响.结果表明,当夹具与槽口的距离在0～40 mm内时,距离值与胶合强度检测值呈一定的线性相关.距离在0～15 mm区间,胶合强度随距离增大呈现增加的趋势,之后则逐步减小.相距15 mm时板的胶合强度最大(1.71 MPa),距离为40 mm时胶合强度最小(1.11 MPa).方差分析的结果表明,夹具与试件槽口的距离对胶合强度检测结果有显著的影响.     

林业中常用的一种分析方法—聚类分析

聚类分析的基本思想是研究的样品或指标（变量）之间存在着的程度不同的相似性（亲疏关系），根据一批样的多个观测指标，具体找出一些能够度量样品或指标之间相似程度的统计量，以此为划分类型的依据，将一些相似程度较大的样品（或指标）聚合在同一类，而将关系疏远的聚合在不同的类，把不同的类型一一划出来，形成一个由小到大的分类系统。最后将整个分类系统绘制成一张聚类图（或称谱系图），并由聚类图进行分类。     

基于自适应邻域Harris算子的三维对象检索方法

针对三维对象检索过程中在对象旋转、灰度改变等复杂情况下检索精度不高的问题,提出一种三维对象检索方法。将Harris算子扩展运用到三维对象,自适应地确定顶点的邻域大小,然后根据Harris函数响应值选取兴趣点。利用兴趣点构建三维对象具有全局形状特征的距离直方图,将距离直方图作为三维形状的描述符进行检索。实验结果验证了算法的有效性,提高了检索的查全率和查准率。     

远程培训助推新农村建设的成效及问题分析---- 基于闽南农村实用技术远程培训状况的调研

农民是将农业科学技术转化为生产力的最终应用者,农村实用技术远程培训可以提高农民应用农业科学技术的效率。对闽南农村实用技术远程培训的现状及成效进行调研后,笔者叙述了农村实用技术远程培训对促进特色农业产业、无公害蔬菜产业、沼气技术产业发展,对促进新农村建设、农村劳动力转移、农民增收致富产生的显著作用,并分析了远程培训存在的亟待解决的问题,提出了采用多渠道弥补远程培训的不足之处,开展区域特色农业远程培训,分层次进行远程培训以满足不同文化水平农民的技术需求、开阔农民的视野、转变农民的观念的对策与建议。     

热处理在果蔬贮藏保鲜中的作用

果蔬贮藏前热处理或贮藏期间歇加温,可以起到防腐、减轻冷害发生等作用,有助于提高果蔬的贮藏效果。作为一项辅助措施,热处理已开始在一些果蔬的贮藏实践中得到应用。     

Impact of livestock and settlement on the large mammalian wildlife of Bale Mountains National Park, southern Ethiopia

Large mammals, both wild and domestic, were censused in four study areas in Bale Mountains National Park (BMNP), southern Ethiopia, from April until August 1997, using established road counts, horse-back counts and systematic transects, a new approach to censusing large mammals in BMNP. Data collected since 1983 were also examined to indicate trends in mammalian abundance. Civil unrest following the government changeover in 1991 disrupted management of BMNP, leading to an increase in human settlement and livestock densities. The effect of these factors on BMNP's wildlife is assessed and discussed. Most large mammalian wildlife has declined since 1983 but signs of recovery for some species in recent years are positive. The fates of two charismatic endemics are emphasised. BMNP's current population of mountain nyala (Tragelaphus buxtoni, an endangered antelope) was estimated to be between 1100 and 1300. This is lower than estimates for the late 1980s, but shows an increase from very low levels recorded following social turmoil during the government changeover in 1991. Data on the Ethiopian wolf (Canis simensis, a critically endangered canid) also indicate positive trends in abundance, following severe declines between 1989 and 1992 due to rabies epizootics. Action to reduce human utilisation of parts of BMNP is urgently required to prevent further degradation of the environment and to safeguard the future of both the mountain nyala and Ethiopian wolf.     

铀钍衰变系核素在土壤侵蚀应用研究的进展

本文对利用铀 ( 2 3 8U)钍 ( 2 3 2 Th)衰变系列中的子体和母体研究泥沙来源和沉积、侵蚀速率的基本原理及应用进行了综述     

Canker and wood rot pathogens present in young lemon orchards in south-west Arizona

Canker and wood rots are economically important preharvest diseases of lemons in south-western Arizona, where commercial lemon production is concentrated. However, the aetiology and epidemiology of canker and wood rots are not well understood. This study comprised a large survey of canker and wood rot incidence and severity in Arizona and the characterization of fungal species associated with the disease. A total of 5431 trees with ages ranging from 1 to 20 years old in 10 lemon orchards were surveyed from 2018 to 2020. Our survey results revealed that canker and wood rot occurred in all 10 lemon orchards studied. Canker and brown rots of twigs, branches, and trunks were the most prevalent symptoms of affected trees ranging from 1 to 20 years old. In contrast, canker and white rots of twigs and branches were observed mostly on 1- to 5-year-old trees. Disease incidence for both diseases was less than 2% on 1- and 2-year-old trees. Brown rot increased significantly in older trees, ranging from 62.9% to 100%. Fungi were isolated from canker and wood rot samples and identified based on morphological characters and DNA sequences. Fomitopsis meliae and Hypoxylon macrocarpum were the primary canker and wood rot pathogens isolated from the surveyed orchards, at frequencies of 89% and 11%, respectively. In pathogenicity tests, both fungi were capable of causing canker and wood rots on lemon cv. Lisbon branches and the necrotic length caused by F. meliae was twofold greater than that caused by H. macrocarpum.     

Formation and decay of ethylenethiourea (ETU) in soil and water under tropical conditions

Mancozeb is a fungicide frequently used in tropical countries. It rapidly decomposes into ethylenethiourea (ETU), a more stable and toxic metabolite than mancozeb that is, therefore, regarded as a pollutant of concern. The objective was to study ETU formation and decay kinetics in soil and water under tropical conditions in order to assess its potential for accumulation. Batch experiments, spiked with either mancozeb or ETU, were carried out under natural (= active) as well as tyndallized conditions. In active soils, dissipation of ETU occurred significantly faster (half‐life 1.5 h) than in tyndallized soils (half‐life time 28 h). In water under natural and sterile conditions, decay was slower than in soils with an ETU half‐life time of 115 and 99 h, respectively. Microbial activity was seen to play an important role in ETU dissipation in soil. However, in water nonbiological processes seem to be more important in the breakdown of the molecule, with hydrolysis being the most probable decay mechanism. Decay of both mancozeb and ETU was found to occur more rapidly than previously reported. The high humidity and temperatures under the simulated humid tropical conditions, and higher microbial activity, lead to more rapid decay of these molecules than under other conditions. Nevertheless, a concentration of 1.29 mg ETU L^–1 was still observed 8 d after adding mancozeb (20.83 mg L^–1) to water under humid tropical conditions. These results suggest that, in comparable regions in the humid tropics, it is unlikely that ETU would accumulate in soil but it represents a potential risk for accumulation in water bodies.