Can you point to some studies that discuss the physical/emotional response to physical intimacy?

I believe I first read about this in a National Geographic article about love. One thing I remember vaguely was something about how women in particular have an emotional response to physical intimacy that makes them feel emotionally close to whomever they were intimate with. This sort of explains the generalization that it is more difficult for women to have sex without attachment. I’m curious to see any other articles or studies about this.