  We associate a t-structure to a family of objects in D(A), the derived
category of a Grothendieck category A. Using general results on t-structures,
we give a new proof of Rickard's theorem on equivalence of bounded derived
categories of modules. Also, we extend this result to bounded derived
categories of quasi-coherent sheaves on separated divisorial schemes obtaining,
in particular, Beilinson's equivalences.
