You could have a radio button to swap between then just have different WHERE clauses

An exact match in Access is one that matches the entire content of the field, i.e. it contains only the word "tea."  But I don't think that is what you intend.  Your intention (I'm guessing) is to match "tea" whenever the word "tea" alone is found somewhere in the field.  E.g.:

My cup of tea
Tea and Sympathy
Boston Tea Party
Coffee or tea?
"Tea"

This is *considerably* more difficult to code.  You have to break down the words individually and find "tea" among them.  Individual words aren't always separated by spaces, as the examples above show.  Words may be preceded with and/or trailed with punctuation marks, preceded with a space or not, trailed with a space or not, etc.  There are tons of conditions to test whether the word "tea" itself (or any word) exist in the field.

Hi Alex, Hi Kevin,
Thank you very much for your fast replies. You understood perfectly what I mean!
I will try to follow these two ideas.
Have a nice day
Rolf

I wonder, whether I can find something about in the Search Seminar before I pay for it?

The search seminar does not cover the advanced logic that Kevin is talking about, I don't believe it covers radio buttons either. But it covers everything else you would need. Then you just need to add one more if/then to it to determine which radio button is selected to determine which where clause to use.

Thanks a lot Adam!