regular expression:- validate string of numbers

hi guys

I am looking for a regular expression which will check if there are
any alphabets in a string of numbers.  
i am using

public function isValidNumber(s:String):Boolean{
return Boolean(s.match(/^[0-9]+$/));
}

if i enter s = 55e or s = 6567y  it returns false which is fine
but when i enter
s = 99.99
it returns false.

When decimal numbers example 99.99 is entered i want it to return true but when
99.aa is entered i want it to return false.

any idea how i can change my above function ?

thanks