青海湖地区耕地演变过程与影响机制分析

通过对青海湖地区耕地总面积、内部结构的变化过程和区域差异的分析，探讨了耕地变化的驱动机制。结果发现该区耕地面积变化呈现出平稳增加、激增、螺旋式增加和锐减的演变趋势，内部结构先呈现水浇地面积的显著增加，浅山地、脑山地相对减少的趋势，然后有出现水浇地和其它类型的耕地此消彼张变化阶段趋势；而耕地变化的区域差异也呈现出全区增长，区域不同步和全区减少的变化趋势。影响研究区耕地变化的原因，除自然因子外，国家大政方针和重大农业政策是导致这种变化的主要原因。     

预切种式木薯排种机构设计与试验

针对当前预切种式木薯播种器存在充种效果差、合格指数低的问题，该研究设计了一种由落种滑板、主动辊筒、型孔摩擦带、支撑辊组、从动辊筒及储种箱等组成的预切种式木薯型孔摩擦带式精密排种机构。阐述了排种机构的基本结构和工作原理。对关键部件参数进行设计，通过理论分析确定影响排种机构充种性能的主要因素为型孔摩擦带型孔形状、型孔数量、型孔摩擦带安装倾角、型孔摩擦带速度以及种茎层厚度。基于离散元法（discrete element method,DEM）建立种茎群-型孔摩擦带仿真模型，通过单因素仿真分析各因素对充种性能及种茎群规律的影响。以充种合格指数和漏充指数为评价指标，通过二次回归正交旋转组合仿真分析确定最优参数，利用Design-Expert数据软件，建立各试验因素与评价指标的数学回归模型，并进行参数优化。结果表明，影响充种合格指数和漏充指数的因素主次顺序为型孔摩擦带速度、型孔摩擦带安装倾角和种茎层厚度，圆整后的最优参数为型孔摩擦带速度0.6 m/s、型孔摩擦带安装倾角45°，种茎层厚度250 mm，此时的模型预测充种合格指数为94.63%，漏充指数为3.42%，重充指数为1.95%。在最优参数下...     

多轴转向车辆转向机构优化设计

多轴转向车辆转向机构是车辆转向时实现内、外轮理想转角关系的核心部件。该文根据汽车车轮转向特性，利用阿克曼定理，应用ADAMS软件建立多轴转向车辆转向机构的仿真模型，同时对转向机构进行了优化。和传统的设计方法相比，这种方法提高了精度和效率。对其它多轴车辆转向机构的优化设计也有一定的参考价值。     

模拟自然条件下黄土区坡地的大气、土表及土壤水交互作用的动力学模型及其应用

The mechanism of atmospheric,surface and soil water interactions( water transformation) in hillslope under natural conditions was analyzed,and a dynamic model was developed to simulate infiltration,overland flow and soil water movement during natural rainfall in hillslope,by bringing froward concepts such as rainfall intensity on slope and a correction coefficient of saturated soil water content for soil surface seal.Some factors,including slope angle,slope orientation and raindrop inclination,which affect the rainfall amount on slope, were taken into account while developing the dynamic model.The effect of surface seal on infiltration and water balance under a boundary condition of the second kind was aslo considered. Application of the model in a field experiment showed that the model simulated precisely the infiltration,overland flow and sol water monvement in hillsope under natural rainfall conditions.     

生物炭和PAM混施影响煤矸石基质水分的入渗和蒸发

探究生物炭和聚丙烯酰胺(PAM)混施对煤矸石基质水分入渗和蒸发的影响,可为矿区矸石山土壤水分的调节提供依据。采用模拟土柱方法,研究不同矸土比(1∶2,1∶1和2∶1)的煤矸石基质,在混施生物炭(1%,2%和4%)和PAM(0.5‰和1‰)条件下,基质水分的吸持性能、入渗及蒸发特征。结果表明:(1)对煤矸石基质入渗性能的影响程度为生物炭PAM矸土比;随生物炭施用量的增加,基质的饱和含水量以及入渗速率均呈增加趋势,而PAM施用量的增加则减弱了煤矸石基质的饱和含水量和入渗速率。(2)添加1‰PAM处理的基质累积蒸发量均低于添加0.5‰PAM的处理;矸土比对煤矸石基质水分蒸发影响程度较生物炭和PAM大。(3)聚类分析表明,4%生物炭和0.5‰PAM混施时煤矸石基质的水分吸持性能及入渗速率较高;而矸土比为2∶1时,2%的生物炭和1‰的PAM混施可减弱基质水分的蒸发。总之,增加生物炭施用量有利于基质水分入渗,而PAM用量的增加,可抑制煤矸石基质水分的蒸发。     

浅议外来植物入侵的途径、机理和危害

对外来植物入侵的途径、机理和危害进行了综述与分析。外来植物入侵受多种因素影响,可分为自然因素和人为因素两类。主要从生态幅、繁殖特性、竞争力、遗传变异特性等方面分析了外来植物入侵的机理。外来植物入侵的危害主要体现在影响当地生态系统的结构和功能、土壤的理化性质、气候、生物多样性、改变物种进化方向和人类的生产与生活等方面。     

Near Crack Line Elastoplastic Solution for an Eccentric Cracks Loaded by the Pore Water Pressure

By using near crack line analysis method and Mohr-Coulomb strength criterion,the elastic-plastic solution for near crack line of an eccentric cracks loaded by the pore water pressure under large scale yielding condition is analyzed.The elastic stress fields,the plastic stress field,the unit normal vector of the elastic-plastic boundary near the crack line,the elastic-plastic stress fields near crack line are identified.The change pattern of the length of the plastic zone and the pore water pressure is presented.Besides,the elastic-plastic analytical solution for an eccentric cracks loaded by the pore water pressure is obtained.     

Effects of water infiltration and storage in cultivated soil on surface irrigation

Surface irrigation analysis and design require the knowledge of the variation of the cumulative infiltration water Z (L) (per unit area) into the soil as a function of the infiltration time t (T). The purpose of this study is to evaluate water infiltration and storage under surface irrigation in an alluvial clay soil cultivated with grape yield, and to determine if partially wetted furrow irrigation has more efficient water storage and infiltration than traditional border irrigation. The two irrigation components considered were wet (WT) and dry (DT) treatments, at which water applied when available soil water reached 65% and 50%, and the traditional border irrigation control. Empirical power form equations were obtained for measured advance and recession times along the furrow length during the irrigation stages of advance, storage, depletion and recession. The infiltration (cumulative depth, Z and rate, I) was functioned to opportunity time (t_o) in minute for WT and DT treatments as: Z_WT = 0.528 t_o^0.6, Z_DT = 1.2 t_o^0.501, I_WT = 19 t_o^−0.4, and I_DT = 36 t_o^−0.498. The irrigation efficiency and soil water distribution have been evaluated using linear distribution and relative schedule depth. Coefficient of variation (CV) was 5.2 and 9.5% for WT and DT under furrow irrigation system comparing with 7.8% in border, respectively. Water was deeply percolated as 11.88 and 19.2% for wet and dry furrow treatments, respectively, compared with 12.8% for control, with no deficit in the irrigated area. Partially wetted furrow irrigation had greater water-efficiency and grape yield than both dry furrow and traditional border irrigations, where application efficiency achieved as 88.1% for wet furrow irrigation that achieved high grape fruit yield (30.71 Mg/ha) and water use efficiency 11.9 kg/m³.     

区域科技文献资源平台共享机制运行实证分析

对我国知名区域科技文献资源平台的共享机制进行了实证分析,拟为各地的区域科技文献资源平台建设提供典型模式及参考。     

农户耕地规模变动机制运行的阶段性

农户耕地规模变动机制的实质为耕地流转型机制，其运行过程呈现出明显的阶段性。在农户数目增加、停滞和减少三个不同阶段，农户耕地规模变动机制运行对农业发展产生了不同影响。我国农户耕地规模变动机制运行尚处在第一阶段，使农业发展不景气。只有促进运行机制的阶段性跃进，才能促进农业的持续发展。对此，政府应采取适当措施。