  Nature, Science, and PNAS are the three most prestigious general-science
journals, and Nature and Science are among the most influential journals
overall, based on the journal Impact Factor (IF). In this paper we perform
automatic classification of ~50,000 articles in these journals (published in
the period 2005-2015) into 14 broad areas, to explore disciplinary profiles and
to determine their field-specific IFs. We find that in all three journals the
articles from Bioscience, Astronomy, and Geosciences are over-represented, with
other areas being under-represented, some of them severely. Discipline-specific
IFs in these journals vary greatly, for example, between 18 and 46 for Nature.
We find that the areas that have the highest disciplinary IFs are not the ones
that contribute the most articles. We also find that publishing articles in
these three journals brings prestige for articles in all areas, but at
different levels, the least being for Astronomy. Comparing field-specific IFs
of Nature, Science and PNAS to other top journals in six largest areas
(Bioscience, Medicine, Geosciences, Physics, Astronomy, and Chemistry) these
three journals are always among the top seven journals, with Nature being at
the very top for all fields except in Medicine.
