经济学家认为知识并不像有形产品，是具有非竞争性的：一个人使用并不会排除他人使用。
Economists think of knowledge, unlike physical goods, as "non-rival" : use by one person does not necessarily preclude use by others.
公共品具备两种特征：一、非排它性：即生产者无法排除购买者以外的其他人使用这一产品，二、非竞争性：意指许多人可以同时使用该产品。
A public good has two attributes: nonexcludability, which means the producer can't prevent the use of the good by others, and nonrivalry, which means that many people can use the good simultaneously.
球管是CT中最昂贵的消耗性核心部件。本文简析了球管的一般常见故障，以及对非致命故障的排除方法。
The tube is the most expensive and consumable part of in spiral CT. This article analysis usual problems, and introduces some preventive maintenance method.
应用推荐