Hi Sue, this should show what you need to do
Are you wanting to use them for joists or as the substrate?
You can definitely use them but there are some considerations. One would be what type of wood to use. Pine and oak immediately come to mind. Perhaps the biggest considerations is using 1”x12” lumber (which is actually 3/4”x11-1/2”). Lumber that wide will want to expand and contract, sometimes to the extreme. It will also want to cup. This can happen even after it has had topcoat applied. This is why real wood flooring (not laminate flooring) is done in thin strips. You can find wider wood flooring but it is normally made with very old wood or ‘sinker wood’ which has been in cold water for an extended period of time. Using thinner lumber would be a wise choice, and hardwood tends to move slightly less than softwood such as pine.
My guess is that your 1"x12"x4' boards are soft wood, which is subject to wear unless a carpet or runner is placed over it. I have 1"x8" to 1"x12" pine and tulip floors throughout our restored 1800's house and my workshop. They were laid down on waxed paper underlayment for wood flooring, which is available in your local flooring or hardware store. I used the spline technique, for which I cutting long straight strips of wood that fit into a grove milled into the length and width of the boards. If you are planning to join the 1"x12"s end to end (i.e. run the boards down the length of the hall) be sure to lay them in staggered patterns joining boards together with splines across the end grain as well as the length of the boards. Attach the boards by blind-nailing the material through the spline and lower part of the of the floorboard grove into the wooden sub-floor every 6 to 8" using a flooring nailer. Another important point to take into consideration is the relative humidity at the time the flooring is laid. Wide boards must be acclimatized and at the same relative humidity as the home. There is much debate around this, but in the north east where I live, I have had the most success laying floors during the transitional seasons of mid fall and very early spring when the air is neither humid or dry so that both shrinkage and expansion at the times of the driest and most humid seasons (mid January and late July) are kept to a minimum. Best of luck.