General

Queries can include the following Boolean operators:

AND, OR, NOT

A query that contains several different operators needs round brackets to remove ambiguities, e.g. osteoporosis and (alcohol or tobacco)

Append field names between square brackets to restrict a search to a particular field. Abbreviations can be found in the [List of field names. Example: smith [au] and array [ti]

Use double quotes to identify phrases (e.g. "red blood cell").

The asterisk functions as a wildcard, replacing any number of characters (e.g. diabet* retrieves diabetes and diabetic). The question mark replaces one single character (e.g. j?nson retrieves Jonson, Jenson, Janson etc.)

Authors

Use the format smith_cp. Author names are automatically expanded to include all combinations of initials, e.g. smith_c returns Smith C, Smith CA etc. You can turn this off by using exact phrase (instead of all words/any word)

Journals

Use the full journal title or standard journal abbreviations (look up here), e.g. Journal of Biology or J Biol Use the checkboxes under 'Include' to specify which major types of BioMed Central content you want to search, or alternatively, select individual journals by following the link to 'Full list of journals'.

Date

You can restrict to recent articles (published within a certain number of days), or you can restrict by year of publication.

Show results

You can use these options to order the results by relevance or date of publication and display more or fewer matches per page.

Storing searches
The search history shows all the searches you have been running in the current session. It is emptied when you close your browser. To store a search for a longer period, click the 'store' button next to the query.

Combining searches
You can combine search numbers from the history with the operators AND, OR and NOT, e.g. #2 and #5 returns articles that are common to search #2 and search #5. You can also combine search numbers with new search terms e.g. #4 NOT jones [au] removes articles by Jones from the results of search #4. You can type combined searches in the advanced search form, or in the boolean search form (only the boolean search page has a list of field names).

Viewing the results of a search
Click the title of the search or click the 'run' button to run the search again and see the results list.