It's not exactly copy and paste but you can import data from Excel using Oracle SQL Developer.
Navigate to the table you want to import the data into and click on the Data tab.
After clicking on the data tab you should notice a drop down that says Actions...

Click Actions... and select the bottom option Import Data...
Then just follow the wizard to select the correct sheet, and columns that you want to import.
EDIT : To view the data tab :
- Select the
SCHEMA where your table is created.(Choose from the Connections tab on the left pane).
- Right click on the
SCHEMA and choose SCHEMA BROWSER.
- Select your table from the list (by giving your schema).
- Now you will see the
DATA tab.
- Click on
Actions and Import Data...