The resistance between the two sides of an outlet should be infinite. The two sides of the outlet are not connected to one another in any fashion as they are two sides of a circuit. The diagram below shows how this works. In an AC circuit, as shown below, the black wire provides AC power, the white is common, and the green is ground. Back in your breaker box, the common wires all go to one buss bar that is to earth ground and the ground wires go to earth ground as well by a separate path making sure that the residual voltage on the common doesn't cross over to the ground wire of another circuit. In the right hand diagram, they show how to connect wires for a series (daisy chain) to another outlet.
So my question is why are you trying to measure resistance here? Normally we would measure voltage. Are you trying to diagnose a circuit problem? In a 110vac system you should have 110vac from black to white and black to green and none from white to green (ideally if nothing is plugged into any outlets). With the breaker off, you should be able to measure the resistance between the two posts on the black side, and that should be 0ohms as they are the same point.