OVID Medline Guide
The search results will now detail the two searches:
The 2 searches can now be combined together usine AND: (click on the play button below to see this action)
This search will search for any article that contains ascorbic acid as a subject heading and common cold limited to preventaion and control as a subheading.
You can combine any set number and even multiple sets. If you had, say, 5 different searchs you could combine 1 and 3 and 5. It depends on what concepts you need to combine for your search.
This above search will produce the following result: