You can combine MeSH and  keywords in PubMed searches. Keywords are particularly useful for finding recent articles.
You should use logic statements such as 

pineal AND thermoregulation

PubMed is programmed to find significant words, and to assume that you want each word in your search to be included in every citation found. Using logic statements is the best way to ensure that PubMed finds what you're looking for when using keywords.

Type in the search pineal AND thermoregulation and click on Go (or press enter).

Click on Details to see how PubMed has searched.

PubMed shows how it has enhanced the search and combined your search terms.

MeSH
PubMed will try to find a MeSH that corresponds to each of your search terms. Notice how the MeSH body temperature regulation has been used to find citations for articles on thermoregulation.

All Fields
Searches all the fields of a PubMed citation except for place of publication and transliterated titles.

Logical Operators
Notice that the words in between the search terms (OR, AND NOT) are in capital letters. These are called logical operators and tell PubMed how to combine the terms entered by the searcher. You must always use capitals for logical operators in PubMed.

Explanation of AND logic
AND logic is used to find citations for articles that include both the terms.

hamburger AND e coli
Finds only those articles that are about both the bacterium E. coli  and hamburger. In the graphic above the green area common to both circles represents the citations with both terms.
 

Explanation of OR logic
OR logic finds citations of journal articles that have any one or more of the terms linked by OR.
A search of thermoregulation OR sweat* OR shivering finds citations that include any one of these terms, any two of these terms or all three of these terms.

Asking Answerable Questions

(on the back of an envelope) Write down the concepts you want to search.
Underneath each concept write down any synonyms or alternative terms you can think of.

pineal	thermoregulation
	shivering

Use the MeSH database to find at least one medical subject heading for each of your concepts.
Also look at the Entry Terms to see if you can find other terms that an authors might use in a title or abstract to describe the content of their articles.

pineal	thermoregulat*
pineal gland	body temperature regulation
epiphysis cerebri	heat loss
	heat losses
	sweat*
	shivering

Now you have a logic grid.

How To Avoid Finding Too Many Irrelevant Citations
Typing topic terms means that PubMed will search in All Fields. This isn't always the most efficient search method because PubMed may find many articles that aren't about your topic.

Instead
first check the MeSH database to find at least one MeSH for each concept you are searching.
Always try to include at least one MeSH in each column if possible. This ensures that you include in your search all the citations indexed by that subject heading and the more specific subject headings.

Add [mh] to your term in your grid to make PubMed search it in the MeSH field

e.g. pineal gland[mh]

Next search for the same term in the titles and abstracts of citations.
Do this by searching
pineal[tiab]

Using [mh] or [tiab] will also ensure that PubMed searches phrases so that heat loss[tiab] will find the exact phrase in the titles and abstracts of citations.
Searching heat loss without the [tiab] will result in a search for heat[all fields] AND loss[all fields] as well as other terms that you might not want.

Include other search terms that might be used by authors in their titles and abstracts to describe the content of their articles.
Including other non MeSH terms for the concept will help you to find citations to articles that don't have MeSH.
Searching in the titles and abstracts of citations is more specific than allowing PubMed to search in All Fileds.

Truncation
PubMed uses the asterisk *, as its truncation symbol.
Adding * to a word stem will get PubMed to search for keywords beginning with the letters that start with the letters to the left of the *.

Never use truncation with MeSH. It interfers with automatic explosion.
You can truncate terms that aren't MeSH as a typing shorthand

e.g. sweat* will find citations that include sweat OR sweated OR sweater OR sweating OR sweats etc

Your logic grid will now look something like this

Join the terms from each column together using OR logic.
Enclose the terms from each column in round brackets.
Use AND logic to combine the searches from the different columns.
Enter the search in the PubMed query box

The logic grid above becomes the search

(pineal[tiab] OR pineal gland[mh] OR epiphysis cerebri[tiab] ) AND (thermoregulat*[tiab] OR body temperature regulation[mh] OR heat loss*[tiab] OR sweat*[tiab] OR shivering[tiab])

Try this search in PubMed and then if you like click on Details to see how the search was conducted.

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