That steroid hormones alter target cell function by binding intracellular receptors is a textbook biological mechanism and foundational fact of endocrinology; no citation is needed.
The claim states a textbook, foundational biological fact regarding the mechanism of action of steroid hormones (binding to intracellular receptors like nuclear receptors to regulate gene transcription and cell function). This is a matter of common scientific knowledge and everyday observation in biology, requiring no empirical citation for verification.