Encyclopedias help you figure out the who, what & where of a topic. Knowing the who, what & where of a topic is the first step in researching a topic and discovering the "how" and "why". Encyclopedias and dictionaries can provide background information and can be used to identify key people, events and dates which can then be used as search terms for finding additional information. Many also provide a jumpstart on your research by listing related readings.
Two online encyclopedia collections: Gale Ebooks & Oxford Reference Online.
These more general encyclopedias on American history and immigration will include material related to the Asian American experience.
These books provide a survey of the state of research about a topic or region, historiography or concise overviews.