The citation contains all relevant reference information (that is, the author, date of publication, journal, title, etc.).
Although every card should contain a complete citation, only the author's name and date of publication are typically cited in a speech.
For that reason, highlighting or underlining once only throughout a year's worth of active debating in tournaments is much preferred practice over re-clipping over the same cards.
Taking the cards during the speech allows the opponent to question the author's qualifications, the original context of the evidence, etc.
Opponents and spectators are also generally allowed to collect citations in this manner and some tournaments send scouts to rounds to facilitate the collection of citation references for every team at the tournament, information which is sometimes published online.