用经验维修法排除拖拉机液压系统的故障

拖拉机安装液压系统优点很多，但出现故障较难排除。为此．采用补偿垫片法、换位法、试调法和排空法等经验维修法排除故障，在使用维护中具有实际应用价值。     

基于内定标法的大豆油中铬含量的LIBS定量分析

为了寻求大豆油中铬(Cr)的快速检测方法,应用激光诱导击穿光谱(LIBS)技术对大豆油中Cr含量进行定量检测研究,采用松木对大豆油样品中的Cr进行富集,并利用双通道光谱仪采集其LIBS光谱信号;选择钙(Ca)422.64 nm为内标线,并以Cr的原子谱线Cr I 425.44 nm、Cr I 427.48 nm、Cr I428.94 nm及3条谱线之和为分析线,应用直接定标法和内定标法分别建立上述分析线的定标曲线。结果表明,Cr I 425.44 nm建立的定标曲线性能最佳,直接定标法和内定标法所建立的定标曲线的拟合度R2分别为0.9598和0.9894,检测限分别为14.82μg·g~(-1)和8.45μg·g~(-1);3个验证样品预测的相对误差分别为11.32%、12.78%、12.48%和7.91%、4.28%、7.64%。由此可知,LIBS技术用于大豆油中重金属Cr的检测具有一定的可行性,松木富集结合内定标法能减少定量分析误差,提高大豆油中Cr含量的预测精度。本研究结果可为食用油中重金属的快速检测提供理论依据。     

Effects of vegetation type on soil resistance to erosion: Relationship between aggregate stability and shear strength

Soil water erosion and shallow landslides depend on aggregate stability and soil shear strength. We investigated the effect of vegetation on both soil aggregate stability and shear strength (through direct shear tests) in former croplands converted to vegetated erosion protection areas within the context of China's sloping land conversion programme. Four treatments were analysed in plots comprised of (i) 4 year old crop trees, Vernicia fordii, where understory vegetation was removed; (ii) V. fordii and the dominant understory species Artemisia codonocephala; (iii) only A. codonocephala and (iv) no vegetation. Soil samples were taken at depths of 0–5 cm and 45–50 cm. Root length density (RLD) in five diameter classes was measured, soil organic carbon (SOC), hot water extractable carbon (HWEC), texture and Fe and Al oxides were also measured. We found that mean weight diameter after slow wetting (MWD_SW) in the A-horizon, was significantly greater (0.94–1.01 mm) when A. codonocephala was present compared to plots without A. codonocephala (0.57–0.59 mm). SOC and RLD in the smallest diameter class (< 0.5 mm), were the variables which best explained variability in MWD_SW. A significant positive linear relationship existed between MWD_SW and soil cohesion but not with internal angle of friction. As herbaceous vegetation was more efficient than trees in improving aggregate stability, this result suggests that the mechanisms involved include modifications of the cohesive forces between soil particles adjacent to plant roots and located in the enriched in SOC rhizosphere, thus also affecting shear strength of the corresponding soil volume. Thus, vegetation stabilised soil under different hierarchical levels of aggregate organisation, i.e. intra- and inter-aggregate. Our results have implications for the efficacy of techniques used in land conversion programs dedicated to control of soil erosion and shallow landslides. We suggest that mixtures of different plant functional types would improve soil conservation on slopes, by reducing both surface water erosion and shallow substrate mass movement. Planting trees for cropping or logging, and removing understory vegetation is most likely detrimental to soil conservation.     

云南咖啡抗锈品种抗锈性丧失原因及防治对策

针对云南咖啡抗锈品种不同植区出现锈病,结合国内锈病小种分布情况,开展了咖啡大田抗锈性丧失原因的调查研究,结果表明:寄主-病原菌-环境的相互作用,使咖啡锈病生理小种不断变异,导致抗锈性丧失,阐述了持久抗锈品种选育研究和合理配置对咖啡品种抗锈持久的重要性,提出了防治锈病的措施。     

龙眼果实采后呼吸强度、细胞膜透性和品质的变化

研究了采后福眼龙眼果实在(20±0.5)和(4±0.5)℃温度下的呼吸强度、细胞膜透性和品质的变化.结果表明:龙眼果实属于非呼吸跃变型果实;在(20±0.5)℃下贮藏2d,果实呼吸强度下降,之后明显上升;果实采后果皮细胞膜透性快速增加,果实易失重、衰老、腐烂和果皮褐变,贮藏后期果肉自溶;果肉可滴定酸和VC含量快速下降,总糖和蔗糖含量下降,还原糖含量先升后降,可溶性固形物含量在贮藏前期下降而后期上升,可溶性固形物和可滴定酸比值先升后降;贮藏后期果肉可滴定酸含量增加.而(4±0.5)℃低温贮藏可显著降低果实呼吸强度,抑制病原菌生长,延缓果实衰老和果皮细胞膜透性增加,延迟果皮褐变,减少果实失重和果肉营养成分变化,抑制果肉自溶,保持果实较高的品质,延长果实贮藏期.     

甜菜机械特性的研究

通过对完整甜菜在电子万能试验机上采用不同的速度进行压缩,得到了完整甜菜的压缩力-位移关系,同时发现在不同的压缩速度下甜菜的破裂位移是不同的,并且通过分析和计算得到了甜菜的破裂点和在不同压缩速度下的刚度,从而为甜菜的收获机械、制糖加工机械的设计以及甜菜制糖工艺提供了相应的力学参数.     

种植密度对玉米茎秆和穗部性状的影响

以郑单958、金海5号为试验材料,研究在中密度(52 500株/hm²)、高密度(75 000株/hm²)条件下对茎秆和穗部性状的影响。结果表明：高密度条件下,两个品种株高和穗位高受影响均不显著,除第1节间茎秆长度显著增加外,其他节间受密度影响不显著,而基部(第3节间)茎的粗度显著减少;中密度条件下,金海5号各节间茎秆穿刺强度均显著大于郑单958。高密度条件下,金海5号各节间茎秆穿刺强度显著减弱,而郑单958除第3节间穿刺强度显著减弱外,其他节间没有明显变化。高密度条件下,穗长、行粒数和百粒重都显著降低。两个品种在高密度下的产量均显著高于中密度。     

补肾活血方对PC 0小鼠未成熟卵母细胞 体外核成熟的影响

〔摘要〕目的探讨补肾活血方对PCO小鼠未成熟卵母细胞体外核成熟的影响、方法(1)制备补肾活血方含药 血清;}2)制作PCO小鼠模型;}3)将PCO小鼠生发泡(germinal vesicle , GV)期卵母细胞分别在不同采血时间获取的 补肾活血方含药血清培养液中进行体外培养,观察补肾活血方含药血清对生发泡破裂(germinal vesicle break- down,GVBD)和第一极体(the first polar body,PBl)排出的时效关系结果(1)2 h和2.5 h药物血清组卵母细胞 GVBD的发生率高于正常血清组和对照组,培养后4 h差异有统计学意义(P<0.01) ; (2)2 h和2.5 h药物血清组卵 母细胞PB1的发生率高于正常血清组和对照组,培养后18 h差异有统计学意义(P<0.01)、结论2-2.5 h补肾活血 方含药血清对PCO小鼠未成熟卵母细胞体外核成熟具有明显促进作用、     

土壤原始颗粒对不同破碎机制下团聚体稳定性的影响

土壤团聚体是土壤结构的基本单元,其稳定性是描述土壤抵抗外力破坏作用的重要指标.目前常用的团聚体测定方法很少考虑到土壤原始颗粒对其不同破碎机制下稳定性的影响.以两种不同质地团聚体特征差异明显的壤质砂土和砂质黏壤土为研究对象,对土壤全样进行快速湿润(FW)、预湿润后震荡(WS)以及慢速湿润(SW)三种处理方式预处理以研究团...