4. The method as claimed in claim 3 , wherein said judging timing is set by a year range n and a condition of 0<n<4 such that said at least one new recent research keyword is defined as a prospective research keyword, and the step of recommending research information further comprises the steps of: calculating how often said prospective research keyword appears in each of said plurality of new recent research documents to obtain a respective prospective index of each of said plurality of new recent research documents, and selecting at least one of said new recent research documents to be set as a prospective research document based on said respective prospective index of each of said new recent research documents.
4. The method as claimed in claim 3 , wherein said judging timing is set by a year range n and a condition of 0<n<4 such that said at least one new recent research keyword is defined as a prospective research keyword, and the step of recommending research information further comprises the steps of: calculating how often said prospective research keyword appears in each of said plurality of new recent research documents to obtain a respective prospective index of each of said plurality of new recent research documents, and selecting at least one of said new recent research documents to be set as a prospective research document based on said respective prospective index of each of said new recent research documents. 5. The method as claimed in claim 4 , wherein said prospective index is attained by the following formula: P = Pr t × We t × ∑ j = 0 n ⁢ TF - IDF j , in which P represents a foreseeing index, Pr t represents a reference source gravity, We t represents a reference source weight, and n represents a year range and meets a condition of 0<n<4.