According to the property of negative integer exponents, for any nonzero number \( a \) and any integer \( n \), the expression \( a^{-n} \) can be rewritten as:
\[ \frac{1}{a^n} \]
Applying this property to \( 9^{-23} \):
\[ 9^{-23} = \frac{1}{9^{23}} \]
Thus, \( 9^{-23} \) rewritten as an expression with positive exponents only is:
\[ \frac{1}{9^{23}} \]