Perhaps you should try some spelling variations:
approximation algorithm » approximation algorithms
invasive estimation » invasive ventilation
seird approximation » time approximation, network approximation
modified invasive » modified passive
modified seird » modified near

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( modified invasive estimation algorithm ) or ( modified seird approximation algorithm ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( modified invasive estimation algorithm ) OR ( modified seird approximation algorithm )).
• Adding a wildcard symbol may retrieve word variants: (( modified invasive estimation algorithm ) or ( modified seird approximation algorithm ))*.