This is a knapsack problem, where the weight of the sack is $n$, and each bid $i$ corresponds to an item of weight $k_i$ and value $d_i$. If each bidder $i$ is unwilling to accept fewer than $k_i$ widgets, then this is a 0/1 problem. If bidders are willing to accept partial lots, on the other hand, then this is a fractional version of the knapsack problem.