I remember there are indexes to indicate publications' impacts. Where do I find those indexes?
The "Web of Science" database is one index for measuring the impact of articles. For each article in search results, "Web of Science" displays a heading "Times Cited:" followed by a number. Click on that number to see citations to the original article.
WEB OF SCIENCE
The "Journal Citation Reports" database can be used to find the impact of a specific journal. In the full entry for each journal, look for the "Cited Journal Data" button to see a list of journals that cite articles published in the journal you are studying.
JOURNAL CITATION REPORTS
Some general information about the influence of a journal can also be found in Cabell's Directories. This source is not particularly useful for the purpose you describe, but it may provide information to supplement "Journal Citation Reports."