As you say, there was no effective resistance to Nazi rule once they had take control of Germany. There are at least two reasons for this.
On one level, the Nazi regime worked hard to keep the German populace happy. The most important example of this is that they did not impose rationing on the people the way the governments of England and the United States did. They did not want to lose support for the war so they kept consumer goods available as long as possible.
However, the regime was also extremely brutal in repressing any opposition. The regime is believed to have killed tens of thousands of people for engaging in various forms of "resistance."
Because of this two-pronged approach, the Nazi regime was very effective in dealing with domestic opposition to its rule.