驱动轴最大静扭强度与表面淬硬层状态关系浅析     

徐成慧  葛便京  李娟子  杨玉 《拖拉机与农用运输车》2011,38(5):82-84

拖拉机驱动轴的最大静扭强度和表面淬硬层状态具有直接关系,并进而直接影响驱动轴的疲劳强度。表面淬硬层不连续会使驱动轴的疲劳强度大幅降低而造成驱动轴早期断裂、失效;驱动轴表面淬硬层不连续会使其最大静扭强度降低30%以上;表面淬硬层过浅也会降低最大静扭强度。  相似文献   

What are the best correlates of predicted extinction risk?     

Julian J. O'Grady  Barry W. Brook 《Biological conservation》2004,118(4):513-520

Direct estimates of extinction risk are frequently unavailable, so surrogate indicators are used in threatened species categorizations, but there is inadequate information on which best predict vulnerability. We compared the ability of 16 frequently-used factors to predict extinction risk for 45 vertebrate taxa. Median times to extinction were estimated using taxon-specific stochastic population models. Population size (N) and trend were clearly the best correlates of extinction risk in our data set. Stepwise multiple regression with additive and interaction terms identified N, N × trend, plus taxonomic level, number of sub-populations × N × trend, number of offspring (O) and N × O as predictors, and explained 70% of the variation. Trend was important in large, but not in small populations. Population size is the most important data to collect for threatened species and with trend should be the major focus in endangered species categorization and state of the environment reporting.  相似文献   

我国《反垄断法》立法中几个基本问题     

周晖 《北京农业职业学院学报》2003,17(1):35-38

目前，我国反垄断方面还没有形成完整的法律体系，制定一部与已有的《反不正当竞争法》相互协调，对市场竞争起到保护和促进作用的《反垄断法》已是当务之急。在此立法中，要明确反垄断法的立法宗旨、反垄断法规范制约的垄断行为、反垄断法的列外、反垄断执法机构的设置与职责，以及垄断行为应承担的法律责任等几个主要问题。  相似文献   

Isolation of Pasteurella haemolytica and correlation with serum antibody response in clinically normal beef calves   总被引：1，自引：0，他引：1  

A W Confer  R E Corstvet  R J Panciera  J A Rummage 《Veterinary microbiology》1983,8(6):601-610

Bacteria from the nasal cavity and trachea were cultured, and serum antibody titers determined for Pasteurella haemolytica serotype 1 in 164 beef calves obtained from a closed herd on range pasture. At the first sampling, P. haemolytica serotype 1 was cultured from 16.4% of the calves. Antibody titers were determined by a quantitative fluorimetric method and the mean titer was 9.5 +/- 5.8. Fifty-seven randomly selected calves were used to study the correlation of serum antibody response and positive culture of P. haemolytica under natural conditions. Clinical signs of respiratory disease were not observed in those calves. During the observation periods, there was a two-fold increase in the percentage of calves that were culture positive. There was no significant difference between mean serum antibody titers or frequency distribution of antibody titers from the two samplings. Comparisons between serum antibody titers, rise in titers, and P. haemolytica isolation failed to reveal any significant correlation. Of the 9 calves that had a decline in antibody titer to P. haemolytica, none was culture positive. Seroconversion to respiratory viruses did not correlate with P. haemolytica related variables.  相似文献   

Developmental changes in trans-permethrin and α-naphthyl acetate ester hydrolysis during the last larval instar of Pseudoplusia includens     

Patrick F. Dowd  Thomas C. Sparks 《Pesticide biochemistry and physiology》1984,21(2):275-282

The hydrolysis of trans-permethrin and α-naphthyl acatate by midgut, fat body, and cuticle homogenates from Pseudoplusia includens (Walker) was monitored during the development of the last instar. The midgut homogenates appeared to have two pH optima (7.6 and 8.6) for the hydrolysis of trans-permethrin, the fat body homogenates had one optimum (7.4–7.8), and the cuticle homogenates had a major optimum at 6.6. Hydrolysis of both substrates peaked during the late feeding stages for midgut and cuticle homogenates, although relative changes were not the same. Hydrolysis of trans-permethrin peaked during the late feeding stage in fat body homogenates, while hydrolysis of α-naphthyl acetate continually increased through the prepupal stage. Thus, the hydrolysis of α-naphthyl acetate is not necessarily associated with the hydrolysis of trans-permethrin. The LD₅₀ values for trans-permethrin on the different stages appeared to reflect the influence of hydrolysis.  相似文献   

甘南草地鼠害现状及防治对策   总被引：4，自引：0，他引：4  

张松林  房妮 《安徽农业科学》2006,34(4):698-699

结合当前鼠害防治的现状,提出了一些合理的鼠害防治措施。  相似文献   

赣南华盛顿脐橙果实发育中几种矿质营养含量动态的研究   总被引：7，自引：1，他引：6  

肖家欣  严翔  彭抒昂  方贻文 《中国生态农业学报》2008,16(1):134-138

赣南红黄壤的土壤条件导致柑橘树体缺素现象比较普遍,而华盛顿脐橙缺素症状并不明显.本文以赣南华盛顿脐橙为试验材料,对其果实发育中果实不同部位(果皮和果肉)的B、Ca、K、Mg和叶片(越冬老叶和当年春梢叶)的B、Ca、K、Mg、Fe、Mn和Zn含量变化进行了对比测定.结果表明:果皮和果肉B含量均于果实膨大期出现显著上升高峰;而对应的Ca含量在幼果期至果实膨大初期相对较高,之后趋明显下降.老叶的B、Ca、Fe和Mn含量均相对稳定,对应春梢叶四者含量均于花后100 d(高温干旱期)出现大幅度下降,之后呈类似的变化趋势;而春梢叶的K、Mg和Zn含量并无此显著下降过程,且老叶的Mg和Zn含量均低于缺乏临界值.  相似文献   

黔东南州植烟土壤及烟叶钼营养评价与相关性分析     

张继  付继刚  潘和平  龙秋蓉 《热带农业科学》2016,(3):53-57

对贵州省黔东南州具有代表性的194个植烟土样的全钼含量、p H值和89个烟叶样本的钼含量进行测定。结果表明:黔东南州植烟土壤全钼含量平均为2.32 mg/kg,烟叶钼含量平均为0.53 mg/kg,土壤全钼含量较为丰富,烟叶钼含量较为缺乏;土壤全钼量与烟叶钼含量呈正相关性,土壤p H与烟叶钼含量呈负相关性,但相关性均未达显著水平。针对黔东南州植烟土壤及烟叶钼含量低的区域,尚需开展进一步的研究与探讨。  相似文献   

贵州省黔东南州退耕还林工程生态效益评估     

谢涛  宋林  赖勇  杨永艳 《安徽农业科学》2016,(31)

运用《退耕还林工程生态效益监测评估技术标准与管理规范》,按照3种植被恢复类型进行测算,对贵州省黔东南州退耕还林工程六大功能的生态效益进行了科学评估。结果表明,截至2015年,黔东南州退耕还林工程的生态效益总价值量为70.68亿元/年,6项生态服务功能价值量从大到小为固碳释氧、涵养水源、保护生物多样性、保育土壤、净化大气环境、林木积累营养物质。通过评估计算,说明黔东南州退耕还林工程发挥的主要生态功能是固碳释氧和涵养水源,分别占总价值量的32.34%和30.76%,工程取得了很好的生态成果。  相似文献   

基于系统耦合的区域生态安全格局构建——以酒泉市肃州区为例   总被引：1，自引：1，他引：0  

──以酒泉市肃州区为例  龙涛  刘学录  黄万状 《中国农学通报》2015,31(5):132-138

构建区域生态安全格局对区域的可持续发展有重要的意义,肃州区位于河西走廊中西部,生态环境脆弱,水资源短缺,生态环境建设与保护形势依然严峻,通过构建区域生态安全格局实现可持续发展尤为重要。通过运用定性、定量相结合的方法分析肃州区的景观格局和景观安全格局。最后,运用系统耦合和景观生态学尺度变化的原理和方法,结合肃州区特点,构建肃州区区域生态安全格局。随着尺度的逐渐变大,区域生态安全格局包括生态资源系统耦合、自然—社会系统耦合、农业生态系统耦合、景观安全格局耦合和生态地理区域耦合5个耦合模式。  相似文献