If necessary I can come at once.

如果有必要，我可以马上来。

《牛津词典》

Shall he come at once?

要不要他马上来？

youdao

I will come at once.

我马上就来。

youdao

Once a month, people come together at a restaurant in Washington to listen to several storytellers perform.

VOA: special.2009.03.27

People can't pay that, if they're in any trouble, they can't come up with the whole value of the loan all at once.

如果人们遇到困难,将无法一次性凑齐这笔大额款项

耶鲁公开课 - 金融市场课程节选

Alright, so maybe a little underwhelming and we saw already what this program is going to do but let's just go through this process once before we start doing more interesting things and then we'll come back and at least give you a hint of what some of these syntactic details are doing.

好吧，这个程序也许太平庸了，让人印象不够深刻,我们也知道这个程序是干嘛的,在我们开始更有意思的事情之前,让我们再来讨论一下整个过程后再回来,这些语法细节到底是在做什么呢？,先给你们一点小小的提示。

哈佛公开课 - 计算机科学课程节选

"The change we seek won't come all at once, from any act of Congress or any executive order signed by the president, " Bush said.

CNN: Bush rallies support for 'faith-based' services package

Eventually, though, everything seemed to come together at once.

NPR: Weak Housing Market May Not Be Signal to Buy

But this has been the pattern of Arsenal's eight barren seasons: Stick around the major competitions long enough to have a shot, then let them all come crashing down at once.

WSJ: Arsenal Back in Its Sticky Patch Again