Perhaps you should try some spelling variations:
ihren grenzgebieten » ihre grenzgebiete
order mathematical » other mathematical, modern mathematical, cover mathematical
ihrer grenzgebiete » ihre grenzgebiete, der grenzgebiete, deren grenzgebiete
der mathematical » her mathematical, mer mathematical, over mathematical
cluster surveys » cluster survey, customer surveys, cluster services
oder surveys » der surveys, other surveys, cover surveys
user surveys » use surveys, user survey, based surveys

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: ergebnisse ((der mathematical) OR (order mathematical)) und ((ihrer grenzgebiete) OR (ihren grenzgebieten)). 2. folge, a series of ((oder surveys) OR (((user surveys) OR (cluster surveys)))) in mathematics.
• The words AND, OR and NOT may confuse the search; try adding quotes: "ergebnisse ((der mathematical) or (order mathematical)) und ((ihrer grenzgebiete) OR (ihren grenzgebieten)). 2. folge, a series of ((oder surveys) or (((user surveys) or (cluster surveys)))) in mathematics".
• Adding a wildcard symbol may retrieve word variants: ergebnisse ((der mathematical) or (order mathematical)) und ((ihrer grenzgebiete) OR (ihren grenzgebieten)). 2. folge, a series of ((oder surveys) or (((user surveys) or (cluster surveys)))) in mathematics*.