Combining searches can be a good way to narrow a search.
Content from this page is from Auburn University's SciFinder LibGuide, by Bob Buchanan, who kindly gave us his permission to re-use it.
1. Use best terms
2. Use prepositions
3. Use parenthetical "OR"
4. Use Analyze / Refine / Categorize to focus or limit results.
The first rule is deceptively simple -- use best terms. It is not as simple, however, to execute; it is hard to know which term will be "best".
There are two types of "best terms": The terms that SciFinder N uses for a concept (indexing and supplementary terms) and the terms that authors use (words in the article title and abstract).
Identifying best terms depends on your chemical knowledge -- as this improves, so, too, will your searches.
Experiment. Try different words to find what works best. Look at the terms used in your best search results, in particular the Indexing concepts and terms in the title and abstract. Incorporate these new terms into your search. It may take several searches (or even weeks or months) to find the best terms.
Be aware that CAS Registry Numbers are almost always better search terms than common names. An exception to this would be a recent reference that has not yet been assigned a CAS Registry Number.
Chemical Abstracts (aka SciFinder N) has a long history of using abbreviations, beginning when printed page space was valuable. Even in the electronic age, Chemical Abstracts continues to use abbreviations. Knowing CAS Abbreviations aids searches.
Sometimes abbreviations are better search terms; LCAO, for example, is better than "linear combination of atomic orbitals". In contrast, HOMO and "highest occupied molecular orbital" are treated identically by SciFinder N.
Using prepositions in SciFinder N results in better search results.
Prepositions invoke the "closely associated" operator, which is a powerful tool.
In SciFinder N, two concepts "closely associated" will be found together in the title of the article, the same sentence in the abstract, the same index term, the same CAS Registry number (and its free-text modifier), or in the list of Supplementary Terms.
There is no guarantee that concepts "closely associated" will be the best, but it is more likely.
To see how SciFinder N searches differently with/without prepositions, compare these three searches:
Be aware that prepositions are not analyzed for their linguistic meaning. In SciFinder N, 'determination of arsenic' is the same as 'determination in arsenic' unless you choose the more restrictive "as entered" phrase results.
SciFinder N does not interpret parentheses in the usual way.
Instead, SciFinder N sees an implied Boolean OR.
For example, "mercaptan (thiol) with electron transfer" would be interpreted by SciFinder as meaning ... "mercaptan with electron transfer OR thiol with electron transfer".
Do not use OR and AND Boolean operators in SciFinder N; they will give quizzical results when used in tandem. Instead, place synonyms after your search term, in parenthesis: mercaptan (thiol).
Analyze
Refine
Categorize
A list of important search points unique to SciFinder -- these apply to no other databases or search engines: