If your partner has not said yes, then your partner has said no, whether he or she uses the word "no" or not.
This concept can be found in the book called Yes Means Yes!: Visions of Female Sexual Power & a World Without Rape. There's also a blog with several contributing bloggers, including the editor of the book, which you can purchase from the blog. The purpose of promoting this campaign is to introduce two concepts: 1) To remove or reduce the grey areas where rape and sexual assault can hide behind ambiguous signals or the victim contributing to his or her own rape; 2) To encourage women in particular, but all people in general, to foster clear communication and embrace their own sexuality by openly and explicitly consenting to sexual activity when sexual activity is desired. There's nothing more attractive in a sexual partner than one who is actively and eagerly engaged in the activities at hand, and there is nothing ambiguous or ambivalent or confusing about a clear and explicit "yes".
Help spread the word that sexual activity should be entered into with active consent only. Because consent is hot!