Calc SS3, the Scientific/Simple (toggle for simple mode) calculator is a great Google Chrome extension for you. If you fancy Apple-like experience, this is a simple way doing it. Once added to Chrome, the Calc SS3 button will shown on the Extensions Bar like the picture below:
What makes it better than the calculator of the iPhone (OS4) is it fixed some weird issues of the original iPhone calculator, explanations can be found here. So check out the Calc SS3 and this is the guide for using the calculator.