child* retrieves records with "child", "children", "childbirth", "childbearing", "childish", and so forth.

Question mark: ?

m?nchen retrieves records with "München" or "Munchen".

Quation marks: "word1 word2"

Default: AND operators between words

"north pole" retrieves only records in which the words "north" and "pole" appear next to each other, in that exact order.

north pole--without quotation marks--retrieves articles with both words "north" and "pole", regardless of where the appear in the document.

AND, OR, NOT.

lincoln AND douglas retrieves articles that contain both "lincoln" and "douglas".

lincoln OR douglas retrieves articles that contain either "lincoln" or "douglas".

"word1 word2"~n
terms inside the quotation marks must appear within n words of eachother, in the specified order.

"henry thoreau"~2 retrieves "henry thoreau", "henry david thoreau", but not "thoreau, henry david".

Pound sign: # 

dostoyevsky~ retrieves articles with "dostoyevsky", as well as variants like "dostoevsky", "dostoievski", "dostoevsky", "dostoyevski", "dostoevskii", "dostoevski", and so forht.

Caret followed by a number: ^n

cat^7 dog gives seven times more weight to the term "cat" than it does "dog".

ti: 

au: