FLT CREW OF CL65 ENCOUNTER NIL BRAKING ON TXWYS AND RAMP.

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LANDED ZZZ RWY FOLLOWING AN ILS APCH. WIND WAS RPTED BY ASOS AS 290 DEGS AT 10 KTS. THE RWY WAS 30% CONTAMINATED BY ICE AND SNOW. BRAKING ACTION WAS GOOD. UPON EXITING THE RWY; I TURNED E THEN SE ONTO TXWY; WHICH I OBSERVED TO BE 100% CONTAMINATED WITH PACKED SNOW. I TAXIED AT MINIMUM SPD; BUT UPON MAKING THE SE TURN THE ACFT BEGAN TO YAW UNCTLABLY TO THE R; WHILE SLIDING L TOWARD THE EDGE OF THE TXWY. BRAKES AND STEERING WERE INEFFECTIVE BUT THE ACFT SLOWED AND CAME TO REST ALIGNED APPROX 30 DEGS CLOCKWISE AND 10 FT L OF TXWY CTRLINE. TAXIING TO THE GATE REQUIRED MINIMUM BRAKING AND LARGE RADIUS TURNS TO MAINTAIN NOSEWHEEL STEERING EFFECTIVENESS. ANY MORE THAN A FEW DEGS OF NOSEWHEEL STEERING CAUSED THE ACFT TO SIMPLY SLIDE FORWARD. THE RAMP AREA WAS ALSO 100% CONTAMINATED WITH ICE AND SNOW AND THE LAST 90 DEGS OF TURN WAS ACCOMPLISHED WITH DIFFICULTY. UPON ARR; I NOTIFIED DISPATCH THAT BRAKING ACTION WAS NIL ON TXWYS AND RAMP. FAILURE TO TREAT THE RAMP OR TXWYS WITH SAND OR DEICE FLUID WILL ULTIMATELY RESULT IN AN ACFT ACCIDENT. I SUGGEST THAT FIELD CONDITION RPTS SIMILAR TO THOSE IN CANADA BE USED; IE; 'RAMP CONTAMINATED WITH 30% PACKED ICE AND SNOW; 10% CLR ICE; REMAINDER CLEAN AND DRY.' SUCH INFO WILL MAKE IT POSSIBLE FOR PLTS AND DISPATCHERS TO DETERMINE IF A FLT CAN BE COMPLETED SAFELY.