SPWebApplication webApp = this.WebApplication;
SPSite site = this.WebApplication.Sites["SiteName"];
SPWeb web = site.OpenWeb("webUrl");
SPList list = web.Lists["ListName"];
foreach (SPListItem item in list.Items)
{
object fieldValue = item["FieldName"];
foreach (SPField field in item.Fields)
{
object fieldValue2 = item[field.Id];
}
}