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Contractually no. Sex is one of a woman's three basic rights in a marriage. (The other two are food and clothing.) And a man also can't force sexual relations on his wife. The argument I've heard is that if there wasn't a separate mitzva (commandment) for a man to pleasure his wife, it never would happen. Whether that's the real logic or just apocryphal I don't know.
However, a woman does not have an absolute right to withhold sex--she can't refuse him as a form of punishment, if she does, her husband can divorce her without paying the hefty divorce settlement required in the kesuba.
Sex is, on the whole, viewed as a very positive and important part of the Jewish marriage. And any stories you may have heard about sex through a hole in a sheet are pure urban legend.