This post is about one class which is very often forgotten or even unknown to many but which exposes some very useful methods.
这个帖子是关于一类，这是经常被遗忘，甚至不知道的很多，但其中暴露出一些非常有用的方法。
The tool is clearly very useful as a way to learn more about people whose usernames you come across online. It's not perfect but it's often quite good.
这项工具非常有用，因为通过这项工具，你可以了解你网上碰到的网名背后此人的更多信息、它还不算完美，但是相当不错了。
You don't always want to use the indirect approach to persuasion, but it's often very useful.
你并不总想用间接的方法来说服对方，但是间接方法确实很有用。
You don’t always want to use the indirect approach to persuasion, but it’s often very useful.
你并不总想用间接的方法来说服对方，但是间接方法确实很有用。
One frustrating problem is the paywall that scholarly archives like JSTOR throw up to non-institutional users, but even the very fact that results turn up in web searches is often useful on its own.
目前非机构用户的一个最大的障碍是学术文档的付费壁垒，像西文过刊全文库；当然，即便如此，网页搜索结果已经很有效了。
The first one that I will mention is actually something you thought maybe you could do with a single integral, but it is useful very often to do it as a double integral.
第一点就是，有些你以为是用一重积分来做的，但却通常是用二重积分来完成的。
Ping is a very useful tool for determining whether or not a machine is accepting packets, but often you want to know more than that, like whether a Web server is actually responding on that machine.
Ping是非常有用的工具，它用于确定机器是否正在接收包，但是通常您想知道的更多，比如Web服务器是否确实响应该机器。
Wave-plate can achieve the purpose of exchanging polarization state and is very useful in the experiment of polarization technology, but it is often influenced by temperature.
波片能够实现偏振态的转换，在偏光技术试验中有重要的作用，但是在使用的过程中其精度会受到温度的影响。
Wave-plate can achieve the purpose of exchanging polarization state and is very useful in the experiment of polarization technology, but it is often influenced by temperature.
波片能够实现偏振态的转换，在偏光技术试验中有重要的作用，但是在使用的过程中其精度会受到温度的影响。
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