The phrase "at once obvious" is correct and usable in written English.
It can be used to indicate that something is immediately clear or evident without any need for further explanation.
Example: "The solution to the problem was at once obvious to everyone in the room."
Alternatives: "immediately clear" or "instantly apparent".
The dynamics are at once obvious and inspired, stroke by stroke and hue by hue, and deliriously affecting — when viewed near at hand.
But there is sufficient ingenuity in the film's main ideas to hold your attention, and the political implications of the allegorical story are at once obvious and subtle.
THE addition of wheat germ to flour lowers its baking quality, as is at once obvious from the smaller volume of the loaf.
Here the production, a most striking one, beats the play, which is a curiosity - at once, obvious, obscure, blatant and convoluted.
The report from the Financial Crisis Inquiry Commission has been assailed as a confusingmishmash - poorly organized, unclear about what's new and weakened by conclusions that are at once obvious and unsatisfying.
Five years after the Egyptian uprising, the role of the armed forces in shaping events is at once obvious and mysterious as it has been for the last 60.
This is at once too obvious to state, and yet, oddly enough, not obvious to millions.
Farrar is at once an obvious and peculiar choice to continue the Mermaid Avenue series.
In the case of politically inspired suicide, the motives are at once more obvious and more elusive.
The transcript illustrates, brilliantly, why the Trump-Russia link, at once so obvious and so unbelievable, has taken so long to sink in.
That sense of something at once utterly obvious and mysteriously fraught with meaning animates the pivotal work in Mr. Koons's career: "Rabbit," from 1986.
