In the circuit given below, V(t) is the sinusoidal voltage source, voltage drop $V_{AB}(t)$ across the resistance R is

Has different peak values during positive and negative half cycle

In positive half cycle one diode is in forward biasing and other is in reverse biasing while in negative half cycle their polarity reverses, and direction of current is opposite through R for positive and negative half cycles so out put is not rectified. Since $R_1$ and $R_2$ are different hence the peaks during positive half and negative half of the input signal will be different.