Perhaps you should try some spelling variations:
"introduction explaining / computer programs" » "introduction exploring / computer programs", "introduction containing / computer programs", "introduction learning / computer programs", "introduction explaining / computer program"
"introduction defining / computer programs" » "introduction containing / computer programs", "introduction defining / computer program"

Try widening your search to All Fields.

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

• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"introduction explaining / computer programs\") OR (\"introduction defining / computer programs\"))".
• Removing quotes may allow a broader search: (( introduction explaining / computer programs ) OR ( introduction defining / computer programs )).
• Adding a wildcard symbol may retrieve word variants: (("introduction explaining / computer programs") OR ("introduction defining / computer programs"))*.