OA publications are predominantly available through gold and green OA
channels, as indicated in earlier sections. Another few models have been
introduced very recently by the commercial publishers for featuring some parts
of their scholarly contents in OA domain. Those are mainly selective open
contents with or without appropriate OA permissions or licenses. Some of the
popular OA models as practiced by the e-journal publishers are: (i) Hybrid
OA, (ii) Delayed OA, (iii) Short-term OA, (iv) Selected OA, and (v) Partial
OA. In hybrid OA model, publishers publish OA articles in toll-access
scholarly journals, after receiving certain article processing charges (APC)
from the authors. In Delayed OA model, publishers offer free access after a
specified period, anywhere from 6 months to 2 years. In Short-term OA model,
publishers offer free access until a specified period, anywhere from 6 months
to 1 year. Then after, contents are available to subscribers only. In Selected OA
model, publishers selectively offer free access to selected contents only. Other
contents are available to subscribers only. In Partial OA model, publishers
selectively offer free access to contents of particular sections only, e.g.,
research papers, but not review papers. Other contents are available to
subscribers only.