Well, it is the stuff that lives in a small box whose base is that piece of surface and whose other side is given by the vector field.

单位时间内的流量就是一个小立体，它的底是曲面上的一块，它的高由向量场给出。

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To create the Person class, click on the class icon in the tool palette and draw a box on the design surface.

要创建person类，单击工具面板上的Class图标，并在设计界面中画一个方框。

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I grabbed an empty box and moved everything from my desk surface to the box.

我拿来了一个空箱子，然后把桌面上的所有东西放了进去。

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Morais received the ball in the box and swept in a low shot along the greasy surface past Howard from just inside the box.

BBC: Inverness CT 2-1 St Mirren

The 64GB version of Surface Pro has 23GB of free storage out of the box.

ENGADGET: 128GB Surface Pro ships with 83GB free, 64GB has only 23GB

Huge swatches of neon yellows, reds and lime-green swiped across every surface try to provide the color-coding necessary to find one's way around within the vast black box.

WSJ: The Library's Future Is Not an Open Book | By Julie V. Iovine | Public Library Renovation