This study evaluates the addition of Ginkgo Diterpene Lactone Meglumine Injection to aspirin in the treatment of acute ischemic stroke.Half of patient will receive Ginkgo Diterpene Lactone Meglumine Injection(25mg once/day D1-D14) and aspirin(300mg loading dose,then 100mg once/day D2-D14) in combination, while the other half will receive aspirin(300mg loading dose,then 100mg once/day D2-D14).