陕西省延安市苜蓿产业状况调查

陕西省延安市苜蓿产业发展过程中存在的问题和制约因素,直接影响了该地区的乳品质量和畜产品安全,必须尽快找出问题的根源,采取有效措施,扭转局面,使草畜产业得以全面发展.阐述了延安市苜蓿产业发展的基本情况、在发展苜蓿产业的扶持政策以及发展过程中所面临的突出问题与制约因素,并提出了推进苜蓿产业发展的措施.     

基于装配特征图树的装配模型与建模方法

通过研究设计信息的映射机理，提出了一种基于装配特征图树的装配模型，并且用符号对其进行了表示，通过建立的特征基本操作的映射算法，可以方例地建立装配模型，实现从功能到结构的映射，而且避免了约速求解中出现的闭环求解的现象，从而实现了概念设计和详细设计的一体化。     

大型轮式拖拉机滚动轴承的装配工艺

大型轮式拖拉机传动系内部轴承装配采用手工砸入的方式,已经不能满足现代企业生产的需要。为了提高传动系统的轴承装配质量,减轻工人的劳动强度,对几种轴承的传统装配工艺进行了技术改造,介绍了改进后的几种装配工艺,并对技术要点进行了分析。     

农业机械底盘机械式变速箱虚拟装配

研究了农业机械的机械式变速箱虚拟装配模型建立方法,并实现了其虚拟装配.将虚拟装配模型分为装配零件固有信息和动态信息的对象模型、装配成员之间层次关系的装配树模型、零部件之间配合约束的关系图模型,通过CAD系统与虚拟装配系统之间的模型数据转换方法获取装配模型信息,在虚拟装配系统中建立装配模型.采用基于空间位置和几何约束的自由度分析法,实现了虚拟装配过程中的运动约束.利用虚拟现实软件EON及其二次开发技术,建立虚拟装配模块,实现了某机械式变速箱的虚拟装配过程.     

良种补贴政策的动因与制约因素探讨——基于水稻作物的实证分析

良种补贴政策施行过程中的主要行为主体是政府部门、农民,还有政府官员及供种工作人员,对该政策的制度设计进行多方多阶段博弈分析,结果表明良种补贴政策在相关约束条件成立的前提下,是可以实现有效均衡的。通过进一步分析相关制约因素发现,在水稻生产函数模型中良种补贴这一政策变量对产量起正向作用(P<0.05),但补贴额度、补贴的对象和方式等方面的限制条件在政策设计之初并未很好地解决。从机制设计角度探讨其根源可以发现,衡量一项公共政策的效率标准首先是必须实现各方参与者的激励相容,而良种补贴政策的实现方式无论对农户和政策执行者都缺乏有效的激励,最终导致政府干预经济效率低下和社会福利损失。     

Closing the cassava yield gap: An analysis from smallholder farms in East Africa

Cassava yields in Africa are small and it remains unclear which factors most limit yields. Using a series of farm surveys and on-farm and on-station trials in Uganda and western Kenya, we evaluated the importance of abiotic, biotic and associated crop management constraints for cassava production in a range of socio-economic settings as found in smallholder farms in the region. Average yields under farmer management were 8.6 t ha⁻¹, but these were more than doubled to 20.8 t ha⁻¹ by using improved crop establishment, improved genotypes and 100–22–83 kg ha⁻¹ of single-nutrient N–P–K fertilizers. A farm survey revealed large yield differences between farms. Less endowed farmers harvested less cassava per unit area than better endowed farmers (difference of 5.9 and 9.7 t ha⁻¹ in Kenya and Uganda, respectively); differences were associated with less access to labour, poorer soils, and premature harvesting by less endowed farmers. Analysis of 99 on-farm and 6 on-station trials showed that constraints for cassava production varied strongly between sites and years. Poor soil fertility, early water stress and sub-optimal weed management limited cassava production by 6.7, 5.4 and 5.0 t ha⁻¹, respectively, when improved crop establishment and genotypes were used. Pests and diseases were relatively unimportant, while weed management was particularly important in farmer fields during a dry year in Kenya (yield gap of 11.6 t ha⁻¹). The use of complementary analytical tools such as multiple regression and boundary line analysis revealed that many fields were affected by multiple and interacting production constraints. These should be addressed simultaneously if significant productivity improvements are to be achieved. This will be more difficult for less endowed than for better endowed farm households, since the former lack social and financial capital to improve management.     

Al toxicity effects on radiation interception and radiation use efficiency of Al-tolerant and Al-sensitive wheat cultivars under field conditions

Soil acidity and Al toxicity are highly extended in agricultural lands of Chile, especially where wheat is widely sown. To evaluate quantitatively the response of wheat biomass and its physiological determinants (intercepted radiation and radiation use efficiency) to Al toxicity, two field experiments were conducted in an Andisol in Valdivia (39°47′S, 73°14′W), Chile, during the 2005–2006 and 2006–2007 growing seasons. Treatments consisted of a factorial arrangement of: (i) two spring wheat cultivars with different sensitivity to Al toxicity (the sensitive cultivar: Domo.INIA and the tolerant cultivar: Dalcahue.INIA) and (ii) five exchangeable Al levels (from 0 to 2.7 cmol₍₊₎ kg⁻¹) with three replicates. Crop phenology and intercepted radiation (IR) were registered during the entire crop cycle, while 10 samples of above-ground biomass were taken at different stages between double ridge and maturity. Both biomass and leaf area index (LAI) were recorded in these 10 stages. Radiation use efficiency (RUE) was calculated as the slope of the relationship between accumulated above-ground biomass and accumulated photosynthetically active radiation intercepted by the canopy (IPARa). Crop phenology was little affected by soil Al treatments, showing only up to 17 days delay in the Al-sensitive cultivar under extreme Al treatments. Above-ground biomass at harvest was closely associated (R² = 0.92) with the crop growth rate but no relationship (R² = 0.14) was found between the crop cycle length. IPARa explained almost completely (R² = 0.93) the above-ground biomass reached by the crop at harvest under the wide range of soil Al concentrations explored in both experiments. On the other hand, a weaker relationship was found between above-ground biomass and RUE. The effect of soil Al concentration on IPARa was mainly explained by LAI as a single relationship (R² = 0.93) between IR (%) and LAI at maximum radiation interception showing a common light attenuation coefficient (k = 0.33).     

新时期促进农业科技创新的对策探讨

阐述了新时期农业科技创新发挥的重要作用,分析了农业科技创新存在的制约因素,并探讨了促进农业科技创新的对策。     

基于一种移动式单工位折叠支架装配台车的研究

企业在批量产品生产制造中大都采用流水线式的装配作业模式,该装配模式具有操作工人劳动强度小、生产效率大幅度提高等优点。但一些部装总成不适宜在流水线上进行装配,存在操作不方便、生产效率低等缺点。针对以上缺点,研究了一种移动式单工位折叠支架装配台车,该装配台车在使用过程中具有结构简单、移动自如、使用方便可靠等特点。     

基于生态约束-发展潜力的城镇建设用地开发适宜性分区

[目的]从生态和经济的角度划分城镇建设用地开发适宜性类型区,为江苏省射阳县土地利用空间布局提供参考。[方法]依据最小累积阻力值分析射阳县区域生态约束强度,划分强度等级;运用多因素多因子综合判别模型,从开发强度和空间距离角度构建评价模型,划分区域发展潜力等级;最终在生态约束等级和发展潜力等级的基础上,进行全域城镇建设用地开发适宜性分区。[结果](1)生态约束高区域与生态约束低的区域相差较大,总体上以生态保护为主。从空间分布上,不同等级强度生态约束力表现出了阶梯式的分布,由内向外辐射,强度逐步提高。(2)开发潜力与生态约束分级结果对比,矛盾突出,经济需求旺盛,生态保护用地形势严峻。(3)适宜保护区、较适宜保护区、较适宜建设区、适宜建设区4类,所占比率分别为11.04%,24.78%,34.59%,29.59%。[结论]开发适宜性分区表现出"核心—边缘"的城乡二元结构特征,同时合德镇及周围的适宜建设区较为集聚,外围适宜建设区逐渐减少。