When you are in the University of Washington's catalog, you must use their commands, not PLU's. The Internet is NOT a universal library catalog or periodical index. You must contact each library and index separately. Not every library has their catalog on the Internet. Nor is every index available on the Internet.
Indexes are commercial products to which libraries subscribe.
Since libraries pay for the databases, they tend to make them available only to their own clientele. There is NO quality control of the Internet. There are many good sites but there are others that may contain opinions, misleading information, or just plain wrong information. The user needs to evaluate each resource found on the Internet. Many journals include articles evaluating Internet sites.