As yet and At present

As yet adverb - Used in negative statement to describe a situation that has existed up to this point or up to the present time.

At present and as yet are semantically related. In some cases you can use "At present" instead an adverb phrase "As yet".

At present adverb - At the present moment.

As yet and at present are semantically related. Sometimes you can replace phrase "As yet" with "At present", this phrases are similar.