Train control system plays a key role in railway traffic. Its function is to manage and control the train movement on ra......

Energy plays an important role in the economic life. With the rapid development of economy, the constraint of energy on ......

社会需求量既决定于收入水平,又受消费倾向所制约.影响消费倾向的因素多种多样,消费能力、消费状态和消费制度是最主要的因素.探讨......