它可以比较粗略地描述成是发生在固定周期（这个周期通常是一年一次）的包含某一个物种很多成员的集体旅行，并且只有在长途旅行后才有回报。

It can loosely be described as travel that takes place at regular intervals—often in an annual cycle—that may involve many members of a species, and is rewarded only after a long journey.

youdao

在这一系列周期性物种灭绝事件里，白垩纪晚期恐龙和菊石的灭绝仅仅是其中一个比较严重的事件。

The late Cretaceous extinction of the dinosaurs and ammonoids was just one of the more drastic in a whole series of such recurrent extinction episodes.

youdao

在比较处于不同周期的不同国家的衰退程度时，这会产生问题。

This can cause problems when trying to compare the depth of downturns in different cycles or across different countries.

youdao

So, if we look on the periodic table, comparing, for example, s to o, if we have s it's below o, what happens to ionization energy as we go down a table?

那么，如果我们看周期表上，比较，比如，硫和氧，硫在氧下面，当我们沿着表向下看的时候,电离能是怎么变化的？

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