开口系统是指系统与外界有物质交换的热力学系统。取系统时只需把所研究的空间范围用边界与外界分隔开来，故又称开口系统为控制体积，简称控制体，其界面为控制界面。
怎样分析开口系统具有重要的理论意义和实用价值。
Analysing open systems are of great important both in theory and in practice.
比较结果表明，对于开口系统SIMPLEC算法综合效果较好，而闭口系统CLEAR算法综合占优。
The results of the comparison show that SIMPLEC is the better algorithm in opened system while CLEAR is better for closed system.
虽然谷歌的系统是一种进步，但它也为“垃圾链接”这种专门用于欺骗系统的弊端提供了开口。
But although Google's system was an improvement, it too was open to abuse from "link spam", created only to dupe the system.
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