https://social.technet.microsoft.com/Forums/en-US/7819a3cc-2b07-4656-aa75-872e400e2629/sharepoint-search-need-to-search-only-list-items?forum=sharepointsearch


 

  1. In search center in results page, click Edit page.
   2. In search results web part, click dropdown in the upper right corner -> click Edit Web Part.
   3. Click Change query -> in Property filter field -> choose contentclass, Contains, Manual value, type STS_ListItem_Announcements  -> click Add property filter.
   4. Repeat Step 3, type contentclass of list items you want to search excluding document, such as STS_ListItem_Comments, STS_ListItem_GenericList, shown as below figure  -> ok


For generic list add 

    "STS_List_GenericList": // Custom List