  An intrinsic relation between maximally entangled states and entanglement
measures is revealed, which plays a role in establishing connections for
different entanglement quantifiers. We exploit the basic idea and propose a
framework to construct schemes for directly measuring entanglement of general
states. In particular, we demonstrate that rank-1 local factorizable projective
measurements, which are achievable with only one copy of entangled state
involved at a time in a sequential way, are sufficient to directly determine
the concurrence of arbitrary two-qubit entangled state.
