"PubMed® comprises more than 30 million citations for biomedical literature from MEDLINE, life science journals, and online books. Citations may include links to full-text content from PubMed Central and publisher web sites." From PubMed. 

Here is a National Library of Medicine's (NLM) tutorial about searching the PubMed interface. PubMed is a freely accessible search database for medically related literature. Although PubMed is free on the web, make sure you access it off Lehigh's library homepage, since you will then see Lehigh Links (mentioned in the Web of Science tutorial).

In the NLM tutorial, the presenter shows you how a PubMed search is mapped into a controlled search vocabulary (thesaurus). The terms in this vocabulary are used in PubMed to index articles, therefore providing a very focused way of searching. You can search in PubMed itself or go directly to the MeSH database. 

Some other tutorials are these:

• Use MeSH to Build a Better PubMed Query
• PubMed: Using the Advanced Search Builder

Some comments: 

• When you search a topic in the MeSH database (MeSH=Medical Subject Headings), you can limit the search to aspects of the topic. Say you want to find literature diagnostic imagining of the brain. You can search on "Brain" in the MeSH, then check off "diagnostic imaging" in the list of subtopics.  
• See the next box below for details relevant to using MeSH terms.
• When you search PubMed, look at the documentation about it. For example, look at these sections in the table of contents.

Searching for a phrase

Truncating search terms

Combining search terms with Boolean operators (AND, OR, NOT)

Below are replies to various questions about the use of Medical Subject Headings (MeSH) terms.  Scroll down to see the original questions.

From: NLM Support <nlm-support@nlm.nih.gov>
Date: Wed, Feb 21, 2024 at 10:28 AM
Subject: Re: case #CAS-1269983-H2F0R3: MeSH Headers TRACKING:000427000004144
To: Brad Simboli <brs4@lehigh.edu>

Thank you for writing to the help desk. 

1.  Typically, NLM does not retroactively re-index MEDLINE citations with new MeSH heading concepts. Therefore, searching PubMed for a new MeSH term tagged with [mh] or [majr] effectively limits retrieval to citations indexed after the term was introduced. Searchers may consult the MeSH database to see the previous indexing terms most likely used for a particular concept before the new MeSH heading was introduced. For terms without previous indexing information, consider the next broader term(s) in the MeSH hierarchy. For more searching guidance, see the on-demand class MeSH Changes and PubMed Searching.

2. Yes, it is important to search using keywords to retrieve relevant items that don't have a new MeSH header or that are not indexed with a MeSH header.

3 & 4. PubMed uses Automatic Term Mapping (https://pubmed.ncbi.nlm.nih.gov/help/#automatic-term-mapping) to help find relevant citations, however it does not search all possible versions or synonyms for every term. You can see how PubMed processed a search by checking the "Search Details" on the Advanced Search page ( https://pubmed.ncbi.nlm.nih.gov/help/#viewing-search-details)

5. Around 31.1 million citations out of 36.8 million total PubMed citations are indexed with MeSH terms. 

Kind regards, 

PubMed Team

National Center for Biotechnology Information

U.S. National Library of Medicine

Details: Hi, I have some questions about MeSH headers:
1 Are new MeSH Headers, when applied in PubMed and Medline, applied retroactively to earlier citations (records)? I might have missed discussion of this question in the NLM help documentation.
2 Is it important to search using both MeSH terms and keywords, in order to pick up items that don't have a new MeSH header or that are not indexed with a MeSH header? (One has to think of an array of keywords though to capture the concept crystallized in the MeSH header.)
3 Does automatic term mapping do this retroactive application of a MeSH term to earlier citations?
4 Can automatic term mapping help in searching for synonyms of a search keyword?
5 Very roughly, what percentage of PubMed or Medline records do not have MeSH headers?
Thanks for any help you can provide. 
Brian Simboli