Filter with SQL statement in Orale Srv?

I have a problem here that some of you out there could give me a n advice. I am wondering whether there is a function provided by Oracle that allows filtering like ‘SELECT …FROM…WHERE…isnumeric’
I am trying to extract from a field(chartype) that I want those are numeric to be converted into numbers. In other words, I am trying to filter out those which contains any nonnumeric characters.
I know that this would be no prob if I’m using Ms SQL Srv 7.
Does anybody out there can help me?