Perhaps you should try some spelling variations:
petriov » petrov (Expand Search), petriiov (Expand Search), petruiov (Expand Search), petroiov (Expand Search)
petruov » petrov (Expand Search), petriuov (Expand Search), petruuov (Expand Search), petrouov (Expand Search)
petris » petri (Expand Search), petriis (Expand Search), petruis (Expand Search), petrois (Expand Search)
petroi » petri (Expand Search), petro (Expand Search), petrov (Expand Search), petrioi (Expand Search), petruoi (Expand Search), petrooi (Expand Search)
petruio » petriuio (Expand Search), petruuio (Expand Search), petrouio (Expand Search)
petr » petri (Expand Search), petru (Expand Search), petro (Expand Search)

Try widening your search to All Fields.

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

• Performing a fuzzy search may retrieve terms with similar spellings: fop ((petriov OR petruov) OR ((((petris OR petris) OR petruio) OR petroi) OR (petr OR peter))) o.s.~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "fop ((petriov OR petruov) OR ((((petris OR petris) OR petruio) OR petroi) OR (petr OR peter))) o.s.".
• Adding a wildcard symbol may retrieve word variants: fop ((petriov OR petruov) OR ((((petris OR petris) OR petruio) OR petroi) OR (petr OR peter))) o.s.*.