yes its possible
i suppose your computer runs win7 or 8, and you have 2 routers; one for each internet connection
first you need to make sure that there will be no IP or gateway conflict between your NICs (Network Interface Controllers/Cards) when you use them simultaneously, and this is done by configuring your routers to use different subnets, because each NIC gets its IP from the router connected to it, ok lets start the routers configuration process, one by one
1- make sure youre connected to one of the routers (only one) through ethernet or wifi
2- open your browser and go to the routers address (usually "192.168.1.1" but if this is not the case refer to the routers manual or visit the manufacturer website for support)
3- enter the routers username (usually "admin") and password (usually "admin" too, or just leave it blanc) to proceed to the configuration page, you can refer to your routers manual or manufacturers website for these too
4- in the routers page look for something like network or LAN settings and open that page
5- now look for something like routers IP, gateway or gateway IP address (it MUST be the same IP you used in step 2; eg. "192.168.1.1") and if you cant find this look for something called subnet (NOT subnet mask, only subnet) and it must be set to same value as the gateway or routers IP except for the last block which must be "0" for the subnet (eg. "192.168.1.0")
6- now after youve found your router/gateway IP address (or subnet), here comes the most important step, you need to change the number in the THIRD block to any OTHER number (x) between 1 and 255 and leave other blocks UNCHANGED, lets say you use 2 instead of 1 this time; eg. "192.168.2.1" for the router/gateway IP or "192.168.2.0" for the subnet
7- look for the "subnet mask" this time and make sure its set to "255.255.255.0", the subnet mask MUST be found on the same page as router/gateway IP or subnet for like 99.99% of routers
8- hit apply or save changes or what so ever, most routers would restart upon changing the subnet
9- if your router didnt restart you need to disconnect your computer from the router and then reconnect to it, in order to get a valid IP address on the new subnet
10- now youre done with the first router
11- disconnect the first router and connect your computer to the other one through wifi or ethernet, and repeat the above steps exactly like you did with the first router, with only one difference: in step 6, when you assign a new number to the third block in your second routers IP or subnet; you need to use a different number than the number you used for the first router (x), dont forget that this number also must be between 1 and 255, lets say you use 3 this time; eg. "192.168.3.1" for router/gateway IP or "192.168.3.0" for the subnet, i strongly recommend you NOT to use "1" for any of your routers, change both of them
now youre done with your routers and there will be no IP conflict between your NICs.
the other thing you need to do is to configure your OS (windows 7/8) to use both NICs and their associated gateways (routers) simultaneously, i.e.; not to "prefer" any NIC over the other, this is easy to do, so lets go
1- go to control panel and open "network and sharing center"
2- click on "change adapter sittings"
3- right click your ethernet adapter icon and choose properties
4- in the networking tap; you will see a set of protocols used by the adapter, scroll down until you see "Internet Protocol version 4 (TCP/IPv4)", double click on it
5- in the general tap, hit advanced
6- in the IP settings tap, uncheck "automatic metric", and set the "interface metric" to 1, click ok to apply and save the new setting
7- do the same thing for "Internet Protocol version 6 (IPv6)", that is; uncheck "automatic metric" and set the "interface metric" to 1, hit ok and close the properties window of the ethernet adapter
8- do exactly the same for the wifi adapter, uncheck "automatic metric" and set the "interface metric" to the same value (1), for both (TCP/IPv4) and (TCP/IPv6), save changes and exit properties
now youre done and you should be able to get the combined bitrate (speed) of both connections
important note: you can get the combined bitrate only in applications that use multible connections like P2P programs, but for browsing or SINGLE video streaming and SINGLE file downloading through ftp (downloading from the web) this is impossible because browsers use one single route to connect to web servers, but you still can make use of the combined bitrate when you download multible files or stream mutible videos