Perhaps you should try some spelling variations:
"multiple operations research : july 2009" » "multiple generations research : july 2009", "multiple migrations research : july 2009", "multiple imputations research : july 2009", "multiple operations research : july 2008", "multiple operations research : july 2007", "multiple operations research : july 2019"
"multiple options research : july 2006" » "multiple locations research : july 2006", "multiple positions research : july 2006", "multiple solutions research : july 2006", "multiple actions research : july 2006", "multiple optics research : july 2006", "multiple options research : july 2008", "multiple options research : july 2007", "multiple options research : july 2013"

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