7. The method of claim 1 , wherein training the first ranking model via machine learning comprises training the first ranking model using the recency features and a plurality of relevance features.
7. The method of claim 1 , wherein training the first ranking model via machine learning comprises training the first ranking model using the recency features and a plurality of relevance features. 9. The method of claim 7 , wherein training the first ranking model using the recency features and the relevance features comprises: accessing a set of relevance ranking data comprising one or more search queries and one or more search results, each of the search results being generated for one of the search queries and comprising one or more network resources; constructing the relevance features from the set of relevance ranking data; determining a first weight for the recency features and a second weight for the relevance features, the first weight indicating a first level of influence the recency features have on training the first ranking model, the second weight indicating a second level of influence the relevance features have on training the first ranking model; and applying the recency features according to the first weight and the relevance features according to the second weight to the first ranking model via machine learning.