For Subject searches try:
Art criticism --History --20th century.
Avant-garde (Aesthetics)--History--20th century.
To do Keyword searches, you can either use add terms or use phrases.
Searching for Art criticism?
Test out art AND criticism or "Art criticism" as searches and see what you can find.
A number of periodicals related to art criticism are available at the Visual Arts Library. Also for articles, you may want to start with indices such as JSTOR & Academic Search Elite or peruse a few serials below.
Art in America
Sight & Sound