Reusing similar requirements fragments is among the promising ways to reduce elaboration time and increase requirements quality. This paper investigates the application of analogical reasoning techniques to complete partial requirements specifications. A case base is assumed to be available; it contains requirements frameworks involving goals, constraints, objects, actions, and agents from systems already specified. We show how a rich requirements meta-model coupled with an expressive formal assertion language may increase the effectiveness of analogical reuse. An acquisition problem is first specified by the requirements engineer as a query formulated in the vocabulary of the specification fragments built so far. Source cases and partial mappings are found by query generalization followed by search through the case base. Once analogies have been confirmed, mappings are completed by use of relevance rules that distinguish in the formal assertions what is relevant to the analogy from what is irrelevant. Best analogies are then selected and extended in such a way that logical properties of the answers to the query may be verified, thus increasing confidence in the analogy. The approach is illustrated by analogical acquisition of specifications of a meeting scheduler in the KAOS goal-oriented specification language.