Perhaps you should try some spelling variations:
"different equations analytical solutions." » "differential equations analytical solutions.", "difference equation analytical solutions.", "differential equation analytical solutions."
"different equations numerical simulation." » "differential equations numerical simulation.", "difference equation numerical simulation.", "differential equation numerical simulation.", "different excitation numerical simulation."

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (("different equations analytical solutions.") OR ("different equations numerical simulation."))~.
• Removing quotes may allow a broader search: (( different equations analytical solutions. ) or ( different equations numerical simulation. ))~.
• Adding a wildcard symbol may retrieve word variants: (("different equations analytical solutions.") or ("different equations numerical simulation."))*.