Search down at the core variant level. Choose > Any Architecture > Core variant. Examples: ARM > Cortex-M3, PPC > E500
Choosing the manufacturer first, reduces the available architectures to simplify your search.
Combine your parametrics with a partial part number or keyword.
If there's a feature you can't see in the pull downs qualify your results with a keyword. These are words specifically added in keyword fields for products and found in their descriptions. (Note: this is not a site search) Examples: Encryption, RS485, LIN (whole words only)