Finally, as part of this contents summary, we must identify the introductory and explanatory materials, which accompany the initial release of methods and practices.

最后，作为内容摘要的一部分，我们必须确定伴随方法和实践最初版本的介绍和说明材料。

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We have learned to look through the contents of the directory, reading chapter summary of the volume, or other support materials to read through the textbooks.

我们已经学会了通过看内容目录，读章卷概要，或其它辅助材料来通读课本的方法。

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Summary: Refractive index is one of the important parameters of optical materials, which often needs to be measured in scientific research and production practice.

摘要：折射率是光学材料的重要参数之一，在科研和生产实际中常需要测量它。

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