Boolean Operators AND, OR, and NOT, or the plus or minus sign can be used within any search field.  Use quotations around a search where you want an exact phrase searched. 

Search using "quotations"

"breast cancer": returns results containing the whole phrase "breast cancer"

Search using a plus or minus sign

HIV: returns results containing HIV
HIV-EIS: returns results containing HIV but omits results containing EIS
HIV-EIS +NHAS: returns results containing both HIV and NHAS, but omits any result containing EIS
HIV-EIS +NHAS -EMA -FOA: returns results containing both HIV and NHAS, but omits results containing any of the following: EIS, EMA, FOA

Search using a plus or minus sign within a word

The plus and minus signs are not interpreted the same way if they are within a word. So funding opportunity numbers and agency names can be directly searched for:
HRSA-13-155: finds all funding opportunities with this agency listed (or have this agency in their description)