http://www.npr.org/2011/08/03/138937778/plagiarism-plague-hi... I don't believe I can put it better than the article above, "These days, China is lavishing money on Mr. Science. But without the checks and balances provided by Mr. Democracy, the corruption plaguing the rest of the system is infecting the reputation of Chinese science. "
Counter point: Dictatorship Germany in WW2 produced many scientific advancements.
And other advancements were... not as impressive as elsewhere. See e.g. nuclear science.
But the upside of science under a dictatorship is that you will publish lots of papers claiming successes, for personal health reasons, so you've got that going for you.
[1] http://www.nejm.org/doi/full/10.1056/NEJM199005173222006