换低速挡

Researches show that the drive force characteristics of the electric tractor drive system based on series DC motor is close the ideal characteristics, the curves are concave, low speed with constant power, and high speed with constant torque; the electric tractor has large working speed under different shifts, but the extensive coincidence speed shows that the variable ratio of the gear is unreasonable; the maximum climbable gradient of this electric tractor is more than 30%, and does not need frequent shift when working for its extensive climbable gradient; there are many influence factors of continuous working time, which the more obvious factors are working speed and working load, the working time increases with the increase of the working speed and working load.2. Simulation researches on the drive characteristic of the electric tractor.

研究结果表明：基于串励直流电动机(来源：ABC21论文网www.abclunwen.com)的电动拖拉机电驱动系统的驱动力特性场接近理想驱动力特性场，其各挡下的驱动力特性是一组下凹的曲线，低速恒转矩，高速恒功率；同一行驶速度下所对应高挡驱动力大于低挡驱动力，这是由电机的调速特性决定的；电动拖拉机各个挡位下具有较广的稳定作业速度范围，但是各个挡位之间速度重合的范围较多，说明所用变速箱变速比与电动机匹配不合理；电动拖拉机最大爬坡度达到30%以上，并且各挡爬坡度变化范围较广，作业过程中不需要频繁换挡；影响电动拖拉机连续作业时间的因素较多，其中作业行驶速度和作业负荷影响最为明显，作业负荷越大，连续作业时间就越短，作业速度越快，连续作业时间就越短。2、电动拖拉机驱动特性仿真研究。

You'll need to change into a low gear on this hill.

你在这处山坡要换成低速挡。

The absorption and distribution of chromium were studied in ryeusing nutrient culture technique and pot experiment.

采用不同浓度K2CrO4(0，0.4，0.8和1.2 mmol/L)的Hoagland营养液处理黑麦幼苗，测定铬在黑麦体内的亚细胞分布、铬化学形态及不同部位的积累。

By analyzing theory foundation of mathematical morphology in the digital image processing, researching morphology arithmetic of the binary Image, discussing two basic forms for the least structure element: dilation and erosion.

通过分析数学形态学在图像中的理论基础，研究二值图像的形态分析算法，探讨最小结构元素的两种基本形态：膨胀和腐蚀；分析了数学形态学复杂算法的基本原理，把数学形态学的部分并行处理理念引入到家实际应用中。