A smile passed fleetingly across his face.

笑容从他的脸上一闪即逝。

《柯林斯英汉双解大词典》

The quarks and gluons indeed break out of confinement and behave collectively, if only fleetingly.

夸克与胶子确实打破牢笼而表现出集体行为，虽然这种状态转瞬即逝。

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One of Friedrich Hayek's obvious-once-pointed-out observations is that society is full of local knowledge, often of a subtle nature and only fleetingly exploitable.

弗里德里希·哈耶克(Friedrich Hayek)曾经指出的一个显而易见的观察就是，社会充满了局部知识，这些知识常常具有微妙特性，以及仅仅是瞬时的可利用性。

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He mentioned Simpson-Bowles fleetingly in his State of the Union speech a month later.

WSJ: Fred Barnes: Obama and the Back-to-the-Future Campaign

Perhaps pity was a truer description of what I felt for him, however fleetingly.

NPR: Sergeant Notes Odd Rituals of War in Afghanistan

What does it say about us that these disgraced politicians have success -- however fleetingly -- after their scandals?

CNN: Zombie politicians find new life after disgrace