Perhaps you should try some spelling variations:
"teaching positions research : july 2011" » "teaching operations research : july 2011", "teaching opinion research : july 2011", "teaching visiting research : july 2011", "teaching positions research : july 2012", "teaching positions research : june 2011"
"call options research : july 2013" » "call operations research : july 2013", "call action research : july 2013", "call opinion research : july 2013", "call option research : july 2013", "real options research : july 2013"

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (("teaching positions research : july 2011") OR ("call options research : july 2013"))~.
• Removing quotes may allow a broader search: (( teaching positions research : july 2011 ) or ( call options research : july 2013 ))~.
• Adding a wildcard symbol may retrieve word variants: (("teaching positions research : july 2011") or ("call options research : july 2013"))*.