Yes, its possible, if you would have create SRD's under Categories then those will be availabe under that category in the Request Entry. And all services will be availble in the request entry but we can not see them all at a time, per page 9 will be displayed if you want see rest you just click on Next button on top right side.
Note that we can see only online services(if you keep some of the SRD's offline those will not be availabe in the Request Entry) in the Request entry.
And if you want see both Online services and as well Offline Services you just follow the below steps.
Goto Home Page --> Service Request Management --> Service Request Designer --> from here you can select Modify button then you will see in the window all SRD's.
I'll illustrate to improve my explanations.
Pic2 - is necessary for me to click on the category icon, so that all services remain visible.
3- Config Perm (service category). The other option is Popular Services.
My doubt is: how do I make visible all the services, all the time?
If you had very low number of SRDs (< 20), you could mark all of them as system favorites on the SRD form ("Yes" in field System Request) and then they would show up in 'Popular Services' view. For a larger number of SRDs in the catalog, this doesn't make sense. Defeats the purpose of 'Popular Services' view.
There is an option to generate a URL that launches SRM Request Entry console in context (see page 320 of SRM 7.6.04 Admin Guide for information about URL builder at SRS:SRCLaunchURLBuilder). You can use this to generate a URL to launch SRM Request Entry console with specific search results displaying, and you can choose to display all SRDs. Use "Services" in field View, and "All" in field Search.