TY  - JOUR
AU  - Zeng Guangxin
TI  - On preordered fields related to Hilbert's 17th problem.
JO  - Mathematische Zeitschrift
PY  - 1991
SP  - 145
EP  - 152
VL  - 206
IS  - 1
PB  - mathdoc
UR  - http://geodesic.mathdoc.fr/item/MZ_1991__206_1_174214/
ID  - MZ_1991__206_1_174214
ER  -