  We investigate theoretically tunable non-Hermitian skin effect in systems
with gain and loss, and find that bipolar (quadripolar) non-Hermitian skin
effect characterized by topological invariants in one (two)-dimensional system.
We also find the partial non-Hermitian skin effect with the coexistence of
localized states and extended states. Both types of the non-Hermitian skin
effect have not yet been predicted together in a single system. A feasible
experimental scheme of our model is proposed to realize in electric circuits.
Our investigation unveils a new type of non-Hermitian skin effect and enhance
the tunability of the non-Hermitian systems by gain and loss other than the
conventional non-reciprocal hopping.
