Perhaps you should try some spelling variations:
"multi operations research : july 2009" » "poultry operations research : july 2009", "port operations research : july 2009", "bus operations research : july 2009", "multi operations research : july 2013", "multi operations research : july 2012", "multi operations research : july 2011"
"multi operations research : july 2006" » "poultry operations research : july 2006", "port operations research : july 2006", "bus operations research : july 2006", "multi operations research : july 2013", "multi operations research : july 2012", "multi operations research : july 2011"

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