%0 Journal Article
%A Zeng Guangxin
%T On preordered fields related to Hilbert's 17th problem.
%J Mathematische Zeitschrift
%D 1991
%P 145-152
%V 206
%N 1
%I mathdoc
%U http://geodesic.mathdoc.fr/item/MZ_1991__206_1_174214/
%F MZ_1991__206_1_174214