Perhaps you should try some spelling variations:
"call options research : july 2009" » "call operations research : july 2009", "call action research : july 2009", "call opinion research : july 2009", "call option research : july 2009", "real options research : july 2009", "call options research : july 2006", "call options research : july 2013", "call options research : july 2011"
"mali options research : july 2012" » "mali operations research : july 2012", "mali action research : july 2012", "mali opinion research : july 2012", "making options research : july 2012", "scale options research : july 2012", "real options research : july 2012", "mali options research : july 2013"

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• Adding a wildcard symbol may retrieve word variants: (("call options research : july 2009") OR ("mali options research : july 2012"))*.