One of the challenges of living in a studio apartment, or in any space short on interior walls, is separating a space into different uses: sleeping, cooking, dining, lounging. It's possible to do this in more subtle ways, like with rugs, but if you prefer to create more concrete divisions, there are ways you can make room dividers work for you (even beyond how you think they can).
In their Chicago studio (above), Franke and Jason used a ubiquitous Kallax bookcase to give visual separation to their small sleeping nook. They filled it with storage bins on the bottom shelves and books on the upper shelves which, because the Kallax doesn't have a backing, allows light and air to filter through but still provides privacy.
In this home (admittedly not a studio but you get the idea) by Forsythe General Contractors, a separation is created between the living room and the other spaces in the house with a room divider that's also a console and a bookcase. In this way the living room is established as a distinct space within the house, without blocking light or views to the other rooms.
You can also do this with a freestanding bookcase, as seen in this studio apartment from Skona Hem.
I just had to include this smart solution from IKEA Hackers, which combines welded sections with Kallax bookcases to create a room divider with a nice bit of transparency.
Speaking of IKEA — their Elvarli system, which adjusts to the height of your space and mounts to the ceiling, makes for a nice transparent room divider — that's also a closet. This might be just the motivation you need to keep all your things highly organized.
If being face-to-face with your entire closet all the time doesn't appeal to you much, you can also use a traditional wardrobe as a room divider, as seen in this space from Hus & Hem.
This image from vtwonen shows a room divider/wardrobe that's open only on one side (and that sits on casters, for maximum flexibility). They also show you how to build it if you're interested in giving it a go.
This DIY from Lana Red Studio shows how you can create a room divider that's also a planter, so you can add a little privacy and a little garden to your space all at the same time.
If you're not the DIYing type, a garment rack outfitted with hanging plants will also get the job done, as seen in this image from K Mart.
If a plain old room divider (or screen) is the only thing you have room for, why not make it into an inspiration board? In this image from VT Wonen, via Jane at Home, the room divider is not just a makeshift wall, but also a design feature in the space.