In this paper we discuss the specific role which ontology can play within an information system intended to support scientific and production activity. We consider methods and scenarios of ontology using and present an approach where ontology is exploited at both development time and run time of information system. We demonstrate how multilingual content-based access to knowledge and information resources of a certain area of knowledge can be provided on the basis of joint use of ontology and thesaurus. This approach was used in the projects aimed at development of scientific knowledge Internet portals on computational linguistics and archeology intended to provide content-based access to systematized knowledge and information resources relevant to the corresponding area of scientific knowledge.