This box may contain one or more keyword or title specifications separated by the + sign. If the box is left empty, no keyword or title restriction will be applied except possibly through the "title" field.
Each keyword/title specification may a single word or a phrase that appears either in the title of the article or book or in the keywords. The reason that both titles and keywords are included is that keywords are usually selected to avoid duplication with words appearing in the title, so a search on keyword alone would miss some relevant publications. If it is a phrase, it must appear exactly as entered (i.e., consecutive words without differences of punctuation; case is ignored).
To find more than one word when you do not know exactly in what order or
combination they appear, use the + sign. For example,
upper limit will only find items
in which those words appear together either in the title or in the same keyword
phrase. But upper + limit will find
"upper confidence limit", "upper credible limit", and "limit of upper bounds"
in either title or keywords. It will also find items with "upper bound" as a
keyword phrase and "limit theorems" in the title.