  We use citation data of scientific articles produced by individual nations in
different scientific domains to determine the structure and efficiency of
national research systems. We characterize the scientific fitness of each
nation (that is, the competitiveness of its research system) and the complexity
of each scientific domain by means of a non-linear iterative algorithm able to
assess quantitatively the advantage of scientific diversification. We find that
technological leading nations, beyond having the largest production of
scientific papers and the largest number of citations, do not specialize in a
few scientific domains. Rather, they diversify as much as possible their
research system. On the other side, less developed nations are competitive only
in scientific domains where also many other nations are present.
Diversification thus represents the key element that correlates with scientific
and technological competitiveness. A remarkable implication of this structure
of the scientific competition is that the scientific domains playing the role
of "markers" of national scientific competitiveness are those not necessarily
of high technological requirements, but rather addressing the most
"sophisticated" needs of the society.
