My bad, the correct shortcut is actually Ctrl + Enter (in fact I did that, but then I wrote the other one) I've updated my comment so that the shortcut is now correct (:
As a matter of fact, the easiest way to copy a pose is to press Space to deselect everything, (and make sure the dopesheet isn't locked or filtered), then select the keyframe in the very first row of the frame you want to select (as this will select all the keyframes below), and copy it.
If you need to paste it in a different animation, you may need to press CTRL+SHIFT+L first, as this creates keys for all the active timelines, then copy the keyframes. (you can later undo the creation of extra keyframes after copying them).
