而在损耗性的种类方面，Raafat (1991)以时间价值来做分类，如下: (1) 固定效用（utility constant）：产品在使用的期限内，它的功能虽然有随时间减弱，但是使用期 间前后的效用并不会有显著的差異，如药水。
基于12个网页-相关网页
You can also use import to introduce other non-constant members as well. For example, consider a math utility library (of questionable value perhaps, but still...) in Listing 6.
也可以使用import来引入其他非常量的成员。
Through constant research and study, the company has won four Utility Model Patent and produced twelve key products.
经过不断探索研究，公司荣获国家实用新型专利四项，重点新产品12项。
Other characteristics, such as frequency, wave shape, and phase balance are seldom recognized by the consumers but are given constant attention by the electric power utility engineers.
而其它方面的特性，如频率、电压波形、各相平衡则很少被用户认识到，但这恰恰受到电力部门工程师们的时刻关注。
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