1. The patent offices of various countries provide download information for national patent texts. Here are a few major ones, all of which are free:
China Office Patent Search and Service System: / sipopublicsearch/portal/index.shtml;
European Patent Office EPO - Searching for patents has extremely comprehensive information and also provides translations in various languages;
US Patent Office Search for Patents ;
WIPO WIPO - Search International and National Patent Collections;
Japan Bureau Patent & Utility Model Gazette DB;
Korean Bureau KIPRIS (Korea Intellectual Property Rights Information Service), Free Patent Information Search Service;
3. Because of the openness of patent information, many of the above search systems include patent information from more than one country. For example, the system of the European Patent Office includes a large amount of patent information from the United States and Japan. Moreover, there are many commercial or non-commercial private websites that also provide comprehensive patent information searches.